forked from Minki/linux
668a6c3654
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
511 lines
13 KiB
C
511 lines
13 KiB
C
/* Support for MMIO probes.
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* Benfit many code from kprobes
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* (C) 2002 Louis Zhuang <louis.zhuang@intel.com>.
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* 2007 Alexander Eichner
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* 2008 Pekka Paalanen <pq@iki.fi>
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*/
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#include <linux/list.h>
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#include <linux/rculist.h>
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#include <linux/spinlock.h>
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#include <linux/hash.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/uaccess.h>
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#include <linux/ptrace.h>
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#include <linux/preempt.h>
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#include <linux/percpu.h>
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#include <linux/kdebug.h>
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#include <linux/mutex.h>
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#include <linux/io.h>
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#include <asm/cacheflush.h>
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#include <asm/tlbflush.h>
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#include <linux/errno.h>
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#include <asm/debugreg.h>
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#include <linux/mmiotrace.h>
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#define KMMIO_PAGE_HASH_BITS 4
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#define KMMIO_PAGE_TABLE_SIZE (1 << KMMIO_PAGE_HASH_BITS)
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struct kmmio_fault_page {
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struct list_head list;
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struct kmmio_fault_page *release_next;
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unsigned long page; /* location of the fault page */
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/*
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* Number of times this page has been registered as a part
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* of a probe. If zero, page is disarmed and this may be freed.
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* Used only by writers (RCU).
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*/
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int count;
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};
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struct kmmio_delayed_release {
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struct rcu_head rcu;
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struct kmmio_fault_page *release_list;
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};
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struct kmmio_context {
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struct kmmio_fault_page *fpage;
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struct kmmio_probe *probe;
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unsigned long saved_flags;
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unsigned long addr;
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int active;
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};
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static DEFINE_SPINLOCK(kmmio_lock);
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/* Protected by kmmio_lock */
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unsigned int kmmio_count;
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/* Read-protected by RCU, write-protected by kmmio_lock. */
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static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE];
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static LIST_HEAD(kmmio_probes);
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static struct list_head *kmmio_page_list(unsigned long page)
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{
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return &kmmio_page_table[hash_long(page, KMMIO_PAGE_HASH_BITS)];
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}
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/* Accessed per-cpu */
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static DEFINE_PER_CPU(struct kmmio_context, kmmio_ctx);
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/*
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* this is basically a dynamic stabbing problem:
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* Could use the existing prio tree code or
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* Possible better implementations:
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* The Interval Skip List: A Data Structure for Finding All Intervals That
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* Overlap a Point (might be simple)
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* Space Efficient Dynamic Stabbing with Fast Queries - Mikkel Thorup
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*/
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/* Get the kmmio at this addr (if any). You must be holding RCU read lock. */
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static struct kmmio_probe *get_kmmio_probe(unsigned long addr)
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{
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struct kmmio_probe *p;
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list_for_each_entry_rcu(p, &kmmio_probes, list) {
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if (addr >= p->addr && addr <= (p->addr + p->len))
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return p;
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}
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return NULL;
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}
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/* You must be holding RCU read lock. */
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static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
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{
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struct list_head *head;
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struct kmmio_fault_page *p;
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page &= PAGE_MASK;
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head = kmmio_page_list(page);
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list_for_each_entry_rcu(p, head, list) {
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if (p->page == page)
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return p;
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}
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return NULL;
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}
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static void set_page_present(unsigned long addr, bool present,
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unsigned int *pglevel)
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{
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pteval_t pteval;
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pmdval_t pmdval;
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unsigned int level;
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pmd_t *pmd;
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pte_t *pte = lookup_address(addr, &level);
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if (!pte) {
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pr_err("kmmio: no pte for page 0x%08lx\n", addr);
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return;
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}
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if (pglevel)
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*pglevel = level;
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switch (level) {
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case PG_LEVEL_2M:
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pmd = (pmd_t *)pte;
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pmdval = pmd_val(*pmd) & ~_PAGE_PRESENT;
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if (present)
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pmdval |= _PAGE_PRESENT;
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set_pmd(pmd, __pmd(pmdval));
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break;
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case PG_LEVEL_4K:
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pteval = pte_val(*pte) & ~_PAGE_PRESENT;
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if (present)
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pteval |= _PAGE_PRESENT;
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set_pte_atomic(pte, __pte(pteval));
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break;
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default:
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pr_err("kmmio: unexpected page level 0x%x.\n", level);
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return;
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}
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__flush_tlb_one(addr);
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}
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/** Mark the given page as not present. Access to it will trigger a fault. */
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static void arm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
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{
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set_page_present(page & PAGE_MASK, false, pglevel);
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}
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/** Mark the given page as present. */
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static void disarm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
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{
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set_page_present(page & PAGE_MASK, true, pglevel);
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}
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/*
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* This is being called from do_page_fault().
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*
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* We may be in an interrupt or a critical section. Also prefecthing may
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* trigger a page fault. We may be in the middle of process switch.
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* We cannot take any locks, because we could be executing especially
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* within a kmmio critical section.
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*
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* Local interrupts are disabled, so preemption cannot happen.
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* Do not enable interrupts, do not sleep, and watch out for other CPUs.
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*/
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/*
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* Interrupts are disabled on entry as trap3 is an interrupt gate
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* and they remain disabled thorough out this function.
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*/
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int kmmio_handler(struct pt_regs *regs, unsigned long addr)
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{
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struct kmmio_context *ctx;
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struct kmmio_fault_page *faultpage;
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int ret = 0; /* default to fault not handled */
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/*
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* Preemption is now disabled to prevent process switch during
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* single stepping. We can only handle one active kmmio trace
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* per cpu, so ensure that we finish it before something else
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* gets to run. We also hold the RCU read lock over single
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* stepping to avoid looking up the probe and kmmio_fault_page
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* again.
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*/
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preempt_disable();
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rcu_read_lock();
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faultpage = get_kmmio_fault_page(addr);
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if (!faultpage) {
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/*
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* Either this page fault is not caused by kmmio, or
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* another CPU just pulled the kmmio probe from under
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* our feet. The latter case should not be possible.
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*/
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goto no_kmmio;
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}
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ctx = &get_cpu_var(kmmio_ctx);
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if (ctx->active) {
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disarm_kmmio_fault_page(faultpage->page, NULL);
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if (addr == ctx->addr) {
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/*
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* On SMP we sometimes get recursive probe hits on the
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* same address. Context is already saved, fall out.
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*/
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pr_debug("kmmio: duplicate probe hit on CPU %d, for "
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"address 0x%08lx.\n",
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smp_processor_id(), addr);
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ret = 1;
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goto no_kmmio_ctx;
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}
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/*
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* Prevent overwriting already in-flight context.
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* This should not happen, let's hope disarming at least
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* prevents a panic.
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*/
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pr_emerg("kmmio: recursive probe hit on CPU %d, "
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"for address 0x%08lx. Ignoring.\n",
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smp_processor_id(), addr);
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pr_emerg("kmmio: previous hit was at 0x%08lx.\n",
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ctx->addr);
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goto no_kmmio_ctx;
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}
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ctx->active++;
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ctx->fpage = faultpage;
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ctx->probe = get_kmmio_probe(addr);
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ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF));
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ctx->addr = addr;
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if (ctx->probe && ctx->probe->pre_handler)
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ctx->probe->pre_handler(ctx->probe, regs, addr);
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/*
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* Enable single-stepping and disable interrupts for the faulting
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* context. Local interrupts must not get enabled during stepping.
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*/
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regs->flags |= X86_EFLAGS_TF;
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regs->flags &= ~X86_EFLAGS_IF;
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/* Now we set present bit in PTE and single step. */
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disarm_kmmio_fault_page(ctx->fpage->page, NULL);
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/*
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* If another cpu accesses the same page while we are stepping,
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* the access will not be caught. It will simply succeed and the
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* only downside is we lose the event. If this becomes a problem,
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* the user should drop to single cpu before tracing.
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*/
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put_cpu_var(kmmio_ctx);
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return 1; /* fault handled */
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no_kmmio_ctx:
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put_cpu_var(kmmio_ctx);
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no_kmmio:
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rcu_read_unlock();
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preempt_enable_no_resched();
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return ret;
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}
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/*
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* Interrupts are disabled on entry as trap1 is an interrupt gate
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* and they remain disabled thorough out this function.
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* This must always get called as the pair to kmmio_handler().
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*/
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static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
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{
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int ret = 0;
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struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx);
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if (!ctx->active) {
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pr_debug("kmmio: spurious debug trap on CPU %d.\n",
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smp_processor_id());
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goto out;
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}
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if (ctx->probe && ctx->probe->post_handler)
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ctx->probe->post_handler(ctx->probe, condition, regs);
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arm_kmmio_fault_page(ctx->fpage->page, NULL);
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regs->flags &= ~X86_EFLAGS_TF;
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regs->flags |= ctx->saved_flags;
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/* These were acquired in kmmio_handler(). */
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ctx->active--;
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BUG_ON(ctx->active);
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rcu_read_unlock();
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preempt_enable_no_resched();
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/*
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* if somebody else is singlestepping across a probe point, flags
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* will have TF set, in which case, continue the remaining processing
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* of do_debug, as if this is not a probe hit.
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*/
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if (!(regs->flags & X86_EFLAGS_TF))
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ret = 1;
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out:
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put_cpu_var(kmmio_ctx);
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return ret;
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}
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/* You must be holding kmmio_lock. */
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static int add_kmmio_fault_page(unsigned long page)
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{
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struct kmmio_fault_page *f;
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page &= PAGE_MASK;
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f = get_kmmio_fault_page(page);
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if (f) {
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if (!f->count)
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arm_kmmio_fault_page(f->page, NULL);
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f->count++;
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return 0;
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}
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f = kmalloc(sizeof(*f), GFP_ATOMIC);
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if (!f)
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return -1;
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f->count = 1;
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f->page = page;
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list_add_rcu(&f->list, kmmio_page_list(f->page));
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arm_kmmio_fault_page(f->page, NULL);
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return 0;
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}
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/* You must be holding kmmio_lock. */
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static void release_kmmio_fault_page(unsigned long page,
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struct kmmio_fault_page **release_list)
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{
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struct kmmio_fault_page *f;
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page &= PAGE_MASK;
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f = get_kmmio_fault_page(page);
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if (!f)
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return;
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f->count--;
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BUG_ON(f->count < 0);
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if (!f->count) {
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disarm_kmmio_fault_page(f->page, NULL);
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f->release_next = *release_list;
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*release_list = f;
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}
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}
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/*
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* With page-unaligned ioremaps, one or two armed pages may contain
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* addresses from outside the intended mapping. Events for these addresses
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* are currently silently dropped. The events may result only from programming
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* mistakes by accessing addresses before the beginning or past the end of a
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* mapping.
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*/
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int register_kmmio_probe(struct kmmio_probe *p)
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{
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unsigned long flags;
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int ret = 0;
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unsigned long size = 0;
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const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
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spin_lock_irqsave(&kmmio_lock, flags);
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if (get_kmmio_probe(p->addr)) {
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ret = -EEXIST;
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goto out;
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}
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kmmio_count++;
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list_add_rcu(&p->list, &kmmio_probes);
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while (size < size_lim) {
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if (add_kmmio_fault_page(p->addr + size))
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pr_err("kmmio: Unable to set page fault.\n");
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size += PAGE_SIZE;
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}
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out:
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spin_unlock_irqrestore(&kmmio_lock, flags);
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/*
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* XXX: What should I do here?
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* Here was a call to global_flush_tlb(), but it does not exist
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* anymore. It seems it's not needed after all.
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*/
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return ret;
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}
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EXPORT_SYMBOL(register_kmmio_probe);
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static void rcu_free_kmmio_fault_pages(struct rcu_head *head)
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{
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struct kmmio_delayed_release *dr = container_of(
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head,
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struct kmmio_delayed_release,
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rcu);
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struct kmmio_fault_page *p = dr->release_list;
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while (p) {
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struct kmmio_fault_page *next = p->release_next;
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BUG_ON(p->count);
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kfree(p);
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p = next;
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}
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kfree(dr);
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}
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static void remove_kmmio_fault_pages(struct rcu_head *head)
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{
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struct kmmio_delayed_release *dr = container_of(
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head,
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struct kmmio_delayed_release,
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rcu);
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struct kmmio_fault_page *p = dr->release_list;
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struct kmmio_fault_page **prevp = &dr->release_list;
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unsigned long flags;
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spin_lock_irqsave(&kmmio_lock, flags);
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while (p) {
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if (!p->count)
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list_del_rcu(&p->list);
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else
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*prevp = p->release_next;
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prevp = &p->release_next;
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p = p->release_next;
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}
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spin_unlock_irqrestore(&kmmio_lock, flags);
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/* This is the real RCU destroy call. */
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call_rcu(&dr->rcu, rcu_free_kmmio_fault_pages);
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}
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/*
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* Remove a kmmio probe. You have to synchronize_rcu() before you can be
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* sure that the callbacks will not be called anymore. Only after that
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* you may actually release your struct kmmio_probe.
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*
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* Unregistering a kmmio fault page has three steps:
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* 1. release_kmmio_fault_page()
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* Disarm the page, wait a grace period to let all faults finish.
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* 2. remove_kmmio_fault_pages()
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* Remove the pages from kmmio_page_table.
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* 3. rcu_free_kmmio_fault_pages()
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* Actally free the kmmio_fault_page structs as with RCU.
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*/
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void unregister_kmmio_probe(struct kmmio_probe *p)
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{
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unsigned long flags;
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unsigned long size = 0;
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const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
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struct kmmio_fault_page *release_list = NULL;
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struct kmmio_delayed_release *drelease;
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spin_lock_irqsave(&kmmio_lock, flags);
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while (size < size_lim) {
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release_kmmio_fault_page(p->addr + size, &release_list);
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size += PAGE_SIZE;
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}
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list_del_rcu(&p->list);
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kmmio_count--;
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spin_unlock_irqrestore(&kmmio_lock, flags);
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drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC);
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if (!drelease) {
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pr_crit("kmmio: leaking kmmio_fault_page objects.\n");
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return;
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}
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drelease->release_list = release_list;
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/*
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* This is not really RCU here. We have just disarmed a set of
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* pages so that they cannot trigger page faults anymore. However,
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* we cannot remove the pages from kmmio_page_table,
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* because a probe hit might be in flight on another CPU. The
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* pages are collected into a list, and they will be removed from
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* kmmio_page_table when it is certain that no probe hit related to
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* these pages can be in flight. RCU grace period sounds like a
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* good choice.
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*
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* If we removed the pages too early, kmmio page fault handler might
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* not find the respective kmmio_fault_page and determine it's not
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* a kmmio fault, when it actually is. This would lead to madness.
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*/
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call_rcu(&drelease->rcu, remove_kmmio_fault_pages);
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}
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EXPORT_SYMBOL(unregister_kmmio_probe);
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static int kmmio_die_notifier(struct notifier_block *nb, unsigned long val,
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void *args)
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{
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struct die_args *arg = args;
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if (val == DIE_DEBUG && (arg->err & DR_STEP))
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if (post_kmmio_handler(arg->err, arg->regs) == 1)
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return NOTIFY_STOP;
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return NOTIFY_DONE;
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}
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static struct notifier_block nb_die = {
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.notifier_call = kmmio_die_notifier
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};
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static int __init init_kmmio(void)
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{
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int i;
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for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++)
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INIT_LIST_HEAD(&kmmio_page_table[i]);
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return register_die_notifier(&nb_die);
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}
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fs_initcall(init_kmmio); /* should be before device_initcall() */
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