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    Subject[tip:x86/xsave] x86, xsave: Use xsaveopt in context-switch path when supported
    Commit-ID:  6bad06b768920e278c7cedfdda56a0b4c6a35ee9
    Gitweb: http://git.kernel.org/tip/6bad06b768920e278c7cedfdda56a0b4c6a35ee9
    Author: Suresh Siddha <suresh.b.siddha@intel.com>
    AuthorDate: Mon, 19 Jul 2010 16:05:52 -0700
    Committer: H. Peter Anvin <hpa@linux.intel.com>
    CommitDate: Mon, 19 Jul 2010 17:52:24 -0700

    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>
    ---
    arch/x86/include/asm/i387.h | 2 +-
    arch/x86/include/asm/xsave.h | 9 ++++++---
    arch/x86/kernel/cpu/common.c | 8 ++++++++
    3 files changed, 15 insertions(+), 4 deletions(-)

    diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
    index bb370fd..59bd93a 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 0c72adc..ec86c5f 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 c735830..3f715ef 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;

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