linux/arch/x86/kernel/fpu/init.c
Andy Lutomirski b9d989c721 x86/asm: Move the thread_info::status field to thread_struct
Because sched.h and thread_info.h are a tangled mess, I turned
in_compat_syscall() into a macro.  If we had current_thread_struct()
or similar and we could use it from thread_info.h, then this would
be a bit cleaner.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jann Horn <jann@thejh.net>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/ccc8a1b2f41f9c264a41f771bb4a6539a642ad72.1473801993.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-09-15 08:25:12 +02:00

393 lines
11 KiB
C

/*
* x86 FPU boot time init code:
*/
#include <asm/fpu/internal.h>
#include <asm/tlbflush.h>
#include <asm/setup.h>
#include <asm/cmdline.h>
#include <linux/sched.h>
#include <linux/init.h>
/*
* Initialize the TS bit in CR0 according to the style of context-switches
* we are using:
*/
static void fpu__init_cpu_ctx_switch(void)
{
if (!boot_cpu_has(X86_FEATURE_EAGER_FPU))
stts();
else
clts();
}
/*
* Initialize the registers found in all CPUs, CR0 and CR4:
*/
static void fpu__init_cpu_generic(void)
{
unsigned long cr0;
unsigned long cr4_mask = 0;
if (boot_cpu_has(X86_FEATURE_FXSR))
cr4_mask |= X86_CR4_OSFXSR;
if (boot_cpu_has(X86_FEATURE_XMM))
cr4_mask |= X86_CR4_OSXMMEXCPT;
if (cr4_mask)
cr4_set_bits(cr4_mask);
cr0 = read_cr0();
cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
if (!boot_cpu_has(X86_FEATURE_FPU))
cr0 |= X86_CR0_EM;
write_cr0(cr0);
/* Flush out any pending x87 state: */
#ifdef CONFIG_MATH_EMULATION
if (!boot_cpu_has(X86_FEATURE_FPU))
fpstate_init_soft(&current->thread.fpu.state.soft);
else
#endif
asm volatile ("fninit");
}
/*
* Enable all supported FPU features. Called when a CPU is brought online:
*/
void fpu__init_cpu(void)
{
fpu__init_cpu_generic();
fpu__init_cpu_xstate();
fpu__init_cpu_ctx_switch();
}
/*
* The earliest FPU detection code.
*
* Set the X86_FEATURE_FPU CPU-capability bit based on
* trying to execute an actual sequence of FPU instructions:
*/
static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
{
unsigned long cr0;
u16 fsw, fcw;
fsw = fcw = 0xffff;
cr0 = read_cr0();
cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
write_cr0(cr0);
if (!test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
asm volatile("fninit ; fnstsw %0 ; fnstcw %1"
: "+m" (fsw), "+m" (fcw));
if (fsw == 0 && (fcw & 0x103f) == 0x003f)
set_cpu_cap(c, X86_FEATURE_FPU);
else
clear_cpu_cap(c, X86_FEATURE_FPU);
}
#ifndef CONFIG_MATH_EMULATION
if (!boot_cpu_has(X86_FEATURE_FPU)) {
pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
for (;;)
asm volatile("hlt");
}
#endif
}
/*
* Boot time FPU feature detection code:
*/
unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
static void __init fpu__init_system_mxcsr(void)
{
unsigned int mask = 0;
if (boot_cpu_has(X86_FEATURE_FXSR)) {
/* Static because GCC does not get 16-byte stack alignment right: */
static struct fxregs_state fxregs __initdata;
asm volatile("fxsave %0" : "+m" (fxregs));
mask = fxregs.mxcsr_mask;
/*
* If zero then use the default features mask,
* which has all features set, except the
* denormals-are-zero feature bit:
*/
if (mask == 0)
mask = 0x0000ffbf;
}
mxcsr_feature_mask &= mask;
}
/*
* Once per bootup FPU initialization sequences that will run on most x86 CPUs:
*/
static void __init fpu__init_system_generic(void)
{
/*
* Set up the legacy init FPU context. (xstate init might overwrite this
* with a more modern format, if the CPU supports it.)
*/
fpstate_init(&init_fpstate);
fpu__init_system_mxcsr();
}
/*
* Size of the FPU context state. All tasks in the system use the
* same context size, regardless of what portion they use.
* This is inherent to the XSAVE architecture which puts all state
* components into a single, continuous memory block:
*/
unsigned int fpu_kernel_xstate_size;
EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);
/* Get alignment of the TYPE. */
#define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
/*
* Enforce that 'MEMBER' is the last field of 'TYPE'.
*
* Align the computed size with alignment of the TYPE,
* because that's how C aligns structs.
*/
#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
TYPE_ALIGN(TYPE)))
/*
* We append the 'struct fpu' to the task_struct:
*/
static void __init fpu__init_task_struct_size(void)
{
int task_size = sizeof(struct task_struct);
/*
* Subtract off the static size of the register state.
* It potentially has a bunch of padding.
*/
task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);
/*
* Add back the dynamically-calculated register state
* size.
*/
task_size += fpu_kernel_xstate_size;
/*
* We dynamically size 'struct fpu', so we require that
* it be at the end of 'thread_struct' and that
* 'thread_struct' be at the end of 'task_struct'. If
* you hit a compile error here, check the structure to
* see if something got added to the end.
*/
CHECK_MEMBER_AT_END_OF(struct fpu, state);
CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
arch_task_struct_size = task_size;
}
/*
* Set up the user and kernel xstate sizes based on the legacy FPU context size.
*
* We set this up first, and later it will be overwritten by
* fpu__init_system_xstate() if the CPU knows about xstates.
*/
static void __init fpu__init_system_xstate_size_legacy(void)
{
static int on_boot_cpu __initdata = 1;
WARN_ON_FPU(!on_boot_cpu);
on_boot_cpu = 0;
/*
* Note that xstate sizes might be overwritten later during
* fpu__init_system_xstate().
*/
if (!boot_cpu_has(X86_FEATURE_FPU)) {
/*
* Disable xsave as we do not support it if i387
* emulation is enabled.
*/
setup_clear_cpu_cap(X86_FEATURE_XSAVE);
setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
fpu_kernel_xstate_size = sizeof(struct swregs_state);
} else {
if (boot_cpu_has(X86_FEATURE_FXSR))
fpu_kernel_xstate_size =
sizeof(struct fxregs_state);
else
fpu_kernel_xstate_size =
sizeof(struct fregs_state);
}
fpu_user_xstate_size = fpu_kernel_xstate_size;
}
/*
* FPU context switching strategies:
*
* Against popular belief, we don't do lazy FPU saves, due to the
* task migration complications it brings on SMP - we only do
* lazy FPU restores.
*
* 'lazy' is the traditional strategy, which is based on setting
* CR0::TS to 1 during context-switch (instead of doing a full
* restore of the FPU state), which causes the first FPU instruction
* after the context switch (whenever it is executed) to fault - at
* which point we lazily restore the FPU state into FPU registers.
*
* Tasks are of course under no obligation to execute FPU instructions,
* so it can easily happen that another context-switch occurs without
* a single FPU instruction being executed. If we eventually switch
* back to the original task (that still owns the FPU) then we have
* not only saved the restores along the way, but we also have the
* FPU ready to be used for the original task.
*
* 'lazy' is deprecated because it's almost never a performance win
* and it's much more complicated than 'eager'.
*
* 'eager' switching is by default on all CPUs, there we switch the FPU
* state during every context switch, regardless of whether the task
* has used FPU instructions in that time slice or not. This is done
* because modern FPU context saving instructions are able to optimize
* state saving and restoration in hardware: they can detect both
* unused and untouched FPU state and optimize accordingly.
*
* [ Note that even in 'lazy' mode we might optimize context switches
* to use 'eager' restores, if we detect that a task is using the FPU
* frequently. See the fpu->counter logic in fpu/internal.h for that. ]
*/
static enum { ENABLE, DISABLE } eagerfpu = ENABLE;
/*
* Find supported xfeatures based on cpu features and command-line input.
* This must be called after fpu__init_parse_early_param() is called and
* xfeatures_mask is enumerated.
*/
u64 __init fpu__get_supported_xfeatures_mask(void)
{
/* Support all xfeatures known to us */
if (eagerfpu != DISABLE)
return XCNTXT_MASK;
/* Warning of xfeatures being disabled for no eagerfpu mode */
if (xfeatures_mask & XFEATURE_MASK_EAGER) {
pr_err("x86/fpu: eagerfpu switching disabled, disabling the following xstate features: 0x%llx.\n",
xfeatures_mask & XFEATURE_MASK_EAGER);
}
/* Return a mask that masks out all features requiring eagerfpu mode */
return ~XFEATURE_MASK_EAGER;
}
/*
* Disable features dependent on eagerfpu.
*/
static void __init fpu__clear_eager_fpu_features(void)
{
setup_clear_cpu_cap(X86_FEATURE_MPX);
}
/*
* Pick the FPU context switching strategy:
*
* When eagerfpu is AUTO or ENABLE, we ensure it is ENABLE if either of
* the following is true:
*
* (1) the cpu has xsaveopt, as it has the optimization and doing eager
* FPU switching has a relatively low cost compared to a plain xsave;
* (2) the cpu has xsave features (e.g. MPX) that depend on eager FPU
* switching. Should the kernel boot with noxsaveopt, we support MPX
* with eager FPU switching at a higher cost.
*/
static void __init fpu__init_system_ctx_switch(void)
{
static bool on_boot_cpu __initdata = 1;
WARN_ON_FPU(!on_boot_cpu);
on_boot_cpu = 0;
WARN_ON_FPU(current->thread.fpu.fpstate_active);
if (boot_cpu_has(X86_FEATURE_XSAVEOPT) && eagerfpu != DISABLE)
eagerfpu = ENABLE;
if (xfeatures_mask & XFEATURE_MASK_EAGER)
eagerfpu = ENABLE;
if (eagerfpu == ENABLE)
setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
printk(KERN_INFO "x86/fpu: Using '%s' FPU context switches.\n", eagerfpu == ENABLE ? "eager" : "lazy");
}
/*
* We parse fpu parameters early because fpu__init_system() is executed
* before parse_early_param().
*/
static void __init fpu__init_parse_early_param(void)
{
if (cmdline_find_option_bool(boot_command_line, "eagerfpu=off")) {
eagerfpu = DISABLE;
fpu__clear_eager_fpu_features();
}
if (cmdline_find_option_bool(boot_command_line, "no387"))
setup_clear_cpu_cap(X86_FEATURE_FPU);
if (cmdline_find_option_bool(boot_command_line, "nofxsr")) {
setup_clear_cpu_cap(X86_FEATURE_FXSR);
setup_clear_cpu_cap(X86_FEATURE_FXSR_OPT);
setup_clear_cpu_cap(X86_FEATURE_XMM);
}
if (cmdline_find_option_bool(boot_command_line, "noxsave"))
fpu__xstate_clear_all_cpu_caps();
if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
setup_clear_cpu_cap(X86_FEATURE_XSAVES);
}
/*
* Called on the boot CPU once per system bootup, to set up the initial
* FPU state that is later cloned into all processes:
*/
void __init fpu__init_system(struct cpuinfo_x86 *c)
{
fpu__init_parse_early_param();
fpu__init_system_early_generic(c);
/*
* The FPU has to be operational for some of the
* later FPU init activities:
*/
fpu__init_cpu();
/*
* But don't leave CR0::TS set yet, as some of the FPU setup
* methods depend on being able to execute FPU instructions
* that will fault on a set TS, such as the FXSAVE in
* fpu__init_system_mxcsr().
*/
clts();
fpu__init_system_generic();
fpu__init_system_xstate_size_legacy();
fpu__init_system_xstate();
fpu__init_task_struct_size();
fpu__init_system_ctx_switch();
}