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Commit 6bad06b7 authored by Suresh Siddha's avatar Suresh Siddha Committed by H. Peter Anvin
Browse files

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



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: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <20100719230205.604014179@sbs-t61.sc.intel.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 29104e10

arch/x86/include/asm/i387.h

+1 −1
Original line number Diff line number Diff line
@@ -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)

arch/x86/include/asm/xsave.h

+6 −3
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/cpu/common.c

+8 −0
Original line number Diff line number Diff line
@@ -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;