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x86, xsave: Use xsaveopt in context-switch path when supported

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xsaveopt is a more optimized form of xsave specifically designed
for the context switch usage. xsaveopt doesn't save the state that's not
modified from the prior xrstor. And if a specific feature state gets
modified to the init state, then xsaveopt just updates the header bit
in the xsave memory layout without updating the corresponding memory
layout.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <20100719230205.604014179@sbs-t61.sc.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Suresh Siddha 2010-07-19 16:05:52 -07:00 committed by H. Peter Anvin
parent 29104e101d
commit 6bad06b768
3 changed files with 15 additions and 4 deletions
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2
arch/x86/include/asm/i387.h
View File

@ -60,7 +60,7 @@ extern int restore_i387_xstate_ia32(void __user *buf);
static __always_inline __pure bool use_xsaveopt(void)
{
return 0;
return static_cpu_has(X86_FEATURE_XSAVEOPT);
}
static __always_inline __pure bool use_xsave(void)

9
arch/x86/include/asm/xsave.h
View File

@ -125,8 +125,11 @@ static inline void fpu_xsave(struct fpu *fpu)
{
/* This, however, we can work around by forcing the compiler to select
an addressing mode that doesn't require extended registers. */
__asm__ __volatile__(".byte " REX_PREFIX "0x0f,0xae,0x27"
: : "D" (&(fpu->state->xsave)),
"a" (-1), "d"(-1) : "memory");
alternative_input(
".byte " REX_PREFIX "0x0f,0xae,0x27",
".byte " REX_PREFIX "0x0f,0xae,0x37",
X86_FEATURE_XSAVEOPT,
[fx] "D" (&fpu->state->xsave), "a" (-1), "d" (-1) :
"memory");
}
#endif

8
arch/x86/kernel/cpu/common.c
View File

@ -140,10 +140,18 @@ EXPORT_PER_CPU_SYMBOL_GPL(gdt_page);
static int __init x86_xsave_setup(char *s)
{
setup_clear_cpu_cap(X86_FEATURE_XSAVE);
setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
return 1;
}
__setup("noxsave", x86_xsave_setup);
static int __init x86_xsaveopt_setup(char *s)
{
setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
return 1;
}
__setup("noxsaveopt", x86_xsaveopt_setup);
#ifdef CONFIG_X86_32
static int cachesize_override __cpuinitdata = -1;
static int disable_x86_serial_nr __cpuinitdata = 1;