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arm64: KVM: Fix stage-2 PGD allocation to have per-page refcounting

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We're using __get_free_pages with to allocate the guest's stage-2
PGD. The standard behaviour of this function is to return a set of
pages where only the head page has a valid refcount.

This behaviour gets us into trouble when we're trying to increment
the refcount on a non-head page:

page:ffff7c00cfb693c0 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x4000000000000000()
page dumped because: VM_BUG_ON_PAGE((*({ __attribute__((unused)) typeof((&page->_count)->counter) __var = ( typeof((&page->_count)->counter)) 0; (volatile typeof((&page->_count)->counter) *)&((&page->_count)->counter); })) <= 0)
BUG: failure at include/linux/mm.h:548/get_page()!
Kernel panic - not syncing: BUG!
CPU: 1 PID: 1695 Comm: kvm-vcpu-0 Not tainted 4.0.0-rc1+ #3825
Hardware name: APM X-Gene Mustang board (DT)
Call trace:
[<ffff80000008a09c>] dump_backtrace+0x0/0x13c
[<ffff80000008a1e8>] show_stack+0x10/0x1c
[<ffff800000691da8>] dump_stack+0x74/0x94
[<ffff800000690d78>] panic+0x100/0x240
[<ffff8000000a0bc4>] stage2_get_pmd+0x17c/0x2bc
[<ffff8000000a1dc4>] kvm_handle_guest_abort+0x4b4/0x6b0
[<ffff8000000a420c>] handle_exit+0x58/0x180
[<ffff80000009e7a4>] kvm_arch_vcpu_ioctl_run+0x114/0x45c
[<ffff800000099df4>] kvm_vcpu_ioctl+0x2e0/0x754
[<ffff8000001c0a18>] do_vfs_ioctl+0x424/0x5c8
[<ffff8000001c0bfc>] SyS_ioctl+0x40/0x78
CPU0: stopping

A possible approach for this is to split the compound page using
split_page() at allocation time, and change the teardown path to
free one page at a time.  It turns out that alloc_pages_exact() and
free_pages_exact() does exactly that.

While we're at it, the PGD allocation code is reworked to reduce
duplication.

This has been tested on an X-Gene platform with a 4kB/48bit-VA host
kernel, and kvmtool hacked to place memory in the second page of
the hardware PGD (PUD for the host kernel). Also regression-tested
on a Cubietruck (Cortex-A7).

 [ Reworked to use alloc_pages_exact() and free_pages_exact() and to
   return pointers directly instead of by reference as arguments
    - Christoffer ]

Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
This commit is contained in:
Marc Zyngier 2015-03-10 19:06:59 +00:00 committed by Christoffer Dall
parent bfb8fb4775
commit a987370f8e
3 changed files with 58 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/arm/include/asm/kvm_mmu.h
View File

@ -162,18 +162,16 @@ static inline bool kvm_page_empty(void *ptr)
#define KVM_PREALLOC_LEVEL 0
static inline int kvm_prealloc_hwpgd(struct kvm *kvm, pgd_t *pgd)
{
return 0;
}
static inline void kvm_free_hwpgd(struct kvm *kvm) { }
static inline void *kvm_get_hwpgd(struct kvm *kvm)
{
return kvm->arch.pgd;
}
static inline unsigned int kvm_get_hwpgd_size(void)
{
return PTRS_PER_S2_PGD * sizeof(pgd_t);
}
struct kvm;
#define kvm_flush_dcache_to_poc(a,l) __cpuc_flush_dcache_area((a), (l))

67
arch/arm/kvm/mmu.c
View File

@ -632,6 +632,20 @@ int create_hyp_io_mappings(void *from, void *to, phys_addr_t phys_addr)
__phys_to_pfn(phys_addr), PAGE_HYP_DEVICE);
}
/* Free the HW pgd, one page at a time */
static void kvm_free_hwpgd(void *hwpgd)
{
free_pages_exact(hwpgd, kvm_get_hwpgd_size());
}
/* Allocate the HW PGD, making sure that each page gets its own refcount */
static void *kvm_alloc_hwpgd(void)
{
unsigned int size = kvm_get_hwpgd_size();
return alloc_pages_exact(size, GFP_KERNEL | __GFP_ZERO);
}
/**
* kvm_alloc_stage2_pgd - allocate level-1 table for stage-2 translation.
* @kvm: The KVM struct pointer for the VM.
@ -645,15 +659,31 @@ int create_hyp_io_mappings(void *from, void *to, phys_addr_t phys_addr)
*/
int kvm_alloc_stage2_pgd(struct kvm *kvm)
{
int ret;
pgd_t *pgd;
void *hwpgd;
if (kvm->arch.pgd != NULL) {
kvm_err("kvm_arch already initialized?\n");
return -EINVAL;
}
hwpgd = kvm_alloc_hwpgd();
if (!hwpgd)
return -ENOMEM;
/* When the kernel uses more levels of page tables than the
* guest, we allocate a fake PGD and pre-populate it to point
* to the next-level page table, which will be the real
* initial page table pointed to by the VTTBR.
*
* When KVM_PREALLOC_LEVEL==2, we allocate a single page for
* the PMD and the kernel will use folded pud.
* When KVM_PREALLOC_LEVEL==1, we allocate 2 consecutive PUD
* pages.
*/
if (KVM_PREALLOC_LEVEL > 0) {
int i;
/*
* Allocate fake pgd for the page table manipulation macros to
* work. This is not used by the hardware and we have no
@ -661,30 +691,32 @@ int kvm_alloc_stage2_pgd(struct kvm *kvm)
*/
pgd = (pgd_t *)kmalloc(PTRS_PER_S2_PGD * sizeof(pgd_t),
GFP_KERNEL | __GFP_ZERO);
if (!pgd) {
kvm_free_hwpgd(hwpgd);
return -ENOMEM;
}
/* Plug the HW PGD into the fake one. */
for (i = 0; i < PTRS_PER_S2_PGD; i++) {
if (KVM_PREALLOC_LEVEL == 1)
pgd_populate(NULL, pgd + i,
(pud_t *)hwpgd + i * PTRS_PER_PUD);
else if (KVM_PREALLOC_LEVEL == 2)
pud_populate(NULL, pud_offset(pgd, 0) + i,
(pmd_t *)hwpgd + i * PTRS_PER_PMD);
}
} else {
/*
* Allocate actual first-level Stage-2 page table used by the
* hardware for Stage-2 page table walks.
*/
pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, S2_PGD_ORDER);
pgd = (pgd_t *)hwpgd;
}
if (!pgd)
return -ENOMEM;
ret = kvm_prealloc_hwpgd(kvm, pgd);
if (ret)
goto out_err;
kvm_clean_pgd(pgd);
kvm->arch.pgd = pgd;
return 0;
out_err:
if (KVM_PREALLOC_LEVEL > 0)
kfree(pgd);
else
free_pages((unsigned long)pgd, S2_PGD_ORDER);
return ret;
}
/**
@ -785,11 +817,10 @@ void kvm_free_stage2_pgd(struct kvm *kvm)
return;
unmap_stage2_range(kvm, 0, KVM_PHYS_SIZE);
kvm_free_hwpgd(kvm);
kvm_free_hwpgd(kvm_get_hwpgd(kvm));
if (KVM_PREALLOC_LEVEL > 0)
kfree(kvm->arch.pgd);
else
free_pages((unsigned long)kvm->arch.pgd, S2_PGD_ORDER);
kvm->arch.pgd = NULL;
}

46
arch/arm64/include/asm/kvm_mmu.h
View File

@ -171,43 +171,6 @@ static inline bool kvm_s2pmd_readonly(pmd_t *pmd)
#define KVM_PREALLOC_LEVEL (0)
#endif
/**
* kvm_prealloc_hwpgd - allocate inital table for VTTBR
* @kvm: The KVM struct pointer for the VM.
* @pgd: The kernel pseudo pgd
*
* When the kernel uses more levels of page tables than the guest, we allocate
* a fake PGD and pre-populate it to point to the next-level page table, which
* will be the real initial page table pointed to by the VTTBR.
*
* When KVM_PREALLOC_LEVEL==2, we allocate a single page for the PMD and
* the kernel will use folded pud. When KVM_PREALLOC_LEVEL==1, we
* allocate 2 consecutive PUD pages.
*/
static inline int kvm_prealloc_hwpgd(struct kvm *kvm, pgd_t *pgd)
{
unsigned int i;
unsigned long hwpgd;
if (KVM_PREALLOC_LEVEL == 0)
return 0;
hwpgd = __get_free_pages(GFP_KERNEL | __GFP_ZERO, PTRS_PER_S2_PGD_SHIFT);
if (!hwpgd)
return -ENOMEM;
for (i = 0; i < PTRS_PER_S2_PGD; i++) {
if (KVM_PREALLOC_LEVEL == 1)
pgd_populate(NULL, pgd + i,
(pud_t *)hwpgd + i * PTRS_PER_PUD);
else if (KVM_PREALLOC_LEVEL == 2)
pud_populate(NULL, pud_offset(pgd, 0) + i,
(pmd_t *)hwpgd + i * PTRS_PER_PMD);
}
return 0;
}
static inline void *kvm_get_hwpgd(struct kvm *kvm)
{
pgd_t *pgd = kvm->arch.pgd;
@ -224,12 +187,11 @@ static inline void *kvm_get_hwpgd(struct kvm *kvm)
return pmd_offset(pud, 0);
}
static inline void kvm_free_hwpgd(struct kvm *kvm)
static inline unsigned int kvm_get_hwpgd_size(void)
{
if (KVM_PREALLOC_LEVEL > 0) {
unsigned long hwpgd = (unsigned long)kvm_get_hwpgd(kvm);
free_pages(hwpgd, PTRS_PER_S2_PGD_SHIFT);
}
if (KVM_PREALLOC_LEVEL > 0)
return PTRS_PER_S2_PGD * PAGE_SIZE;
return PTRS_PER_S2_PGD * sizeof(pgd_t);
}
static inline bool kvm_page_empty(void *ptr)