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: 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>

3 files changed, 15 insertions, 4 deletions

diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index bb370fd0a1c2..59bd93ac7fef 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -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)
diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
index 0c72adc0cb15..ec86c5fd6a6e 100644
--- a/arch/x86/include/asm/xsave.h
+++ b/arch/x86/include/asm/xsave.h
@@ -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
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index c7358303d8cd..3f715efc594d 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -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;