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    Subject[tip:x86/xsave] x86, xsave: Make xstate_enable_boot_cpu() __init, protect on CPU 0
    Commit-ID:  1cff92d8fdb27684308864d9cdb324bee43b40ab
    Gitweb: http://git.kernel.org/tip/1cff92d8fdb27684308864d9cdb324bee43b40ab
    Author: H. Peter Anvin <hpa@linux.intel.com>
    AuthorDate: Wed, 21 Jul 2010 14:23:10 -0700
    Committer: H. Peter Anvin <hpa@linux.intel.com>
    CommitDate: Wed, 21 Jul 2010 15:33:54 -0700

    x86, xsave: Make xstate_enable_boot_cpu() __init, protect on CPU 0

    xstate_enable_boot_cpu() is, as the name implies, only used on the
    boot CPU; furthermore, it invokes alloc_bootmem(), which is __init;
    hence it needs to be tagged __init rather than __cpuinit.

    Furthermore, it is *not* safe in the long run to rely on CPU 0 only
    coming online during the early boot -- at some point we're going to
    support offlining (and re-onlining) the boot CPU, and at that point we
    must not call xstate_enable_boot_cpu() again.

    The code is a fair bit more obscure than one would like, because the
    __ref overrides aren't quite powerful enough.

    Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
    Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
    Cc: Robert Richter <robert.richter@amd.com>
    LKML-Reference: <4C476236.1020302@zytor.com>
    ---
    arch/x86/kernel/xsave.c | 28 +++++++++++++++++-----------
    1 files changed, 17 insertions(+), 11 deletions(-)

    diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
    index cfc7901..b2549c3 100644
    --- a/arch/x86/kernel/xsave.c
    +++ b/arch/x86/kernel/xsave.c
    @@ -360,10 +360,10 @@ unsigned int sig_xstate_size = sizeof(struct _fpstate);
    /*
    * Enable the extended processor state save/restore feature
    */
    -static inline void xstate_enable(u64 mask)
    +static inline void xstate_enable(void)
    {
    set_in_cr4(X86_CR4_OSXSAVE);
    - xsetbv(XCR_XFEATURE_ENABLED_MASK, mask);
    + xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
    }

    /*
    @@ -421,7 +421,7 @@ static void __init setup_xstate_init(void)
    /*
    * Enable and initialize the xsave feature.
    */
    -static void __cpuinit xstate_enable_boot_cpu(void)
    +static void __init xstate_enable_boot_cpu(void)
    {
    unsigned int eax, ebx, ecx, edx;

    @@ -444,7 +444,7 @@ static void __cpuinit xstate_enable_boot_cpu(void)
    */
    pcntxt_mask = pcntxt_mask & XCNTXT_MASK;

    - xstate_enable(pcntxt_mask);
    + xstate_enable();

    /*
    * Recompute the context size for enabled features
    @@ -462,16 +462,22 @@ static void __cpuinit xstate_enable_boot_cpu(void)
    pcntxt_mask, xstate_size);
    }

    +/*
    + * For the very first instance, this calls xstate_enable_boot_cpu();
    + * for all subsequent instances, this calls xstate_enable().
    + *
    + * This is somewhat obfuscated due to the lack of powerful enough
    + * overrides for the section checks.
    + */
    void __cpuinit xsave_init(void)
    {
    + static __refdata void (*next_func)(void) = xstate_enable_boot_cpu;
    + void (*this_func)(void);
    +
    if (!cpu_has_xsave)
    return;

    - /*
    - * Boot processor to setup the FP and extended state context info.
    - */
    - if (!smp_processor_id())
    - xstate_enable_boot_cpu();
    - else
    - xstate_enable(pcntxt_mask);
    + this_func = next_func;
    + next_func = xstate_enable;
    + this_func();
    }

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