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    Subject[tip:x86/apic] x86/apic: Avoid open coded x2apic detection
    Commit-ID:  8d80696060eedf49c080c0f2cf39a20ae7e787f9
    Gitweb: http://git.kernel.org/tip/8d80696060eedf49c080c0f2cf39a20ae7e787f9
    Author: Thomas Gleixner <tglx@linutronix.de>
    AuthorDate: Thu, 15 Jan 2015 21:22:09 +0000
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Thu, 22 Jan 2015 15:10:54 +0100

    x86/apic: Avoid open coded x2apic detection

    enable_IR_x2apic() grew a open coded x2apic detection. Implement a
    proper helper function which shares the code with the already existing
    x2apic_enabled().

    Made it use rdmsrl_safe as suggested by Boris.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Jiang Liu <jiang.liu@linux.intel.com>
    Cc: Joerg Roedel <joro@8bytes.org>
    Cc: Tony Luck <tony.luck@intel.com>
    Link: http://lkml.kernel.org/r/20150115211702.285038186@linutronix.de
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    arch/x86/include/asm/apic.h | 19 ++++++++++---------
    arch/x86/kernel/apic/apic.c | 5 +----
    2 files changed, 11 insertions(+), 13 deletions(-)

    diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
    index 465b309..1a8ba26 100644
    --- a/arch/x86/include/asm/apic.h
    +++ b/arch/x86/include/asm/apic.h
    @@ -108,6 +108,15 @@ extern u64 native_apic_icr_read(void);

    extern int x2apic_mode;

    +static inline bool apic_is_x2apic_enabled(void)
    +{
    + u64 msr;
    +
    + if (rdmsrl_safe(MSR_IA32_APICBASE, &msr))
    + return false;
    + return msr & X2APIC_ENABLE;
    +}
    +
    #ifdef CONFIG_X86_X2APIC
    /*
    * Make previous memory operations globally visible before
    @@ -175,15 +184,7 @@ extern void check_x2apic(void);
    extern void enable_x2apic(void);
    static inline int x2apic_enabled(void)
    {
    - u64 msr;
    -
    - if (!cpu_has_x2apic)
    - return 0;
    -
    - rdmsrl(MSR_IA32_APICBASE, msr);
    - if (msr & X2APIC_ENABLE)
    - return 1;
    - return 0;
    + return cpu_has_x2apic && apic_is_x2apic_enabled();
    }

    #define x2apic_supported() (cpu_has_x2apic)
    diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
    index 35e6d09..7ecfce1 100644
    --- a/arch/x86/kernel/apic/apic.c
    +++ b/arch/x86/kernel/apic/apic.c
    @@ -1625,10 +1625,7 @@ void __init enable_IR_x2apic(void)
    int ret, ir_stat;

    if (!IS_ENABLED(CONFIG_X86_X2APIC)) {
    - u64 msr;
    -
    - rdmsrl(MSR_IA32_APICBASE, msr);
    - if (msr & X2APIC_ENABLE)
    + if (apic_is_x2apic_enabled())
    panic("BIOS has enabled x2apic but kernel doesn't support x2apic, please disable x2apic in BIOS.\n");
    }


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