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    Subject[PATCH 1/5] x86-32: use symbolic constants, safer CPUID when enabling EFER.NX
    Date
    Use symbolic constants rather than hard-coded values when setting
    EFER.NX in head_32.S, and do a more rigorous test for the validity of
    the response when probing for the extended CPUID range.

    Signed-off-by: H. Peter Anvin <hpa@zytor.com>
    ---
    arch/x86/kernel/head_32.S | 18 +++++++++++-------
    1 files changed, 11 insertions(+), 7 deletions(-)

    diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
    index 050c278..7fd318b 100644
    --- a/arch/x86/kernel/head_32.S
    +++ b/arch/x86/kernel/head_32.S
    @@ -18,6 +18,8 @@
    #include <asm/asm-offsets.h>
    #include <asm/setup.h>
    #include <asm/processor-flags.h>
    +#include <asm/msr-index.h>
    +#include <asm/cpufeature.h>
    #include <asm/percpu.h>

    /* Physical address */
    @@ -297,25 +299,27 @@ ENTRY(startup_32_smp)
    orl %edx,%eax
    movl %eax,%cr4

    - btl $5, %eax # check if PAE is enabled
    - jnc 6f
    + testb $X86_CR4_PAE, %al # check if PAE is enabled
    + jz 6f

    /* Check if extended functions are implemented */
    movl $0x80000000, %eax
    cpuid
    - cmpl $0x80000000, %eax
    - jbe 6f
    + /* Value must be in the range 0x80000001 to 0x8000ffff */
    + subl $0x80000001, %eax
    + cmpl $(0x8000ffff-0x80000001), %eax
    + ja 6f
    mov $0x80000001, %eax
    cpuid
    /* Execute Disable bit supported? */
    - btl $20, %edx
    + btl $(X86_FEATURE_NX & 31), %edx
    jnc 6f

    /* Setup EFER (Extended Feature Enable Register) */
    - movl $0xc0000080, %ecx
    + movl $MSR_EFER, %ecx
    rdmsr

    - btsl $11, %eax
    + btsl $_EFER_NX, %eax
    /* Make changes effective */
    wrmsr

    --
    1.6.2.5


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