Re: [Xen-devel] [PATCH] x86/microcode: Use native_cpuid() in load_ucode_amd_bsp()

[Borislav Petkov <bp@xxxxxxxxx>]

On Fri, Dec 16, 2016 at 11:39:52AM -0500, Boris Ostrovsky wrote:
> When CONFIG_PARAVIRT is selected, cpuid() becomes a call. Since
> for 32-bit kernels load_ucode_amd_bsp() is executed before paging
> is enabled the call cannot be completed (as kernel virtual addresses
> are not reachable yet).
> 
> Use native_cpuid() instead which is an asm wrapper for CPUID instruction.
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/microcode/amd.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/amd.c 
> b/arch/x86/kernel/cpu/microcode/amd.c
> index 6f353bd..e2d941f 100644
> --- a/arch/x86/kernel/cpu/microcode/amd.c
> +++ b/arch/x86/kernel/cpu/microcode/amd.c
> @@ -297,6 +297,7 @@ void __init load_ucode_amd_bsp(unsigned int family)
>       struct cpio_data cp;
>       const char *path;
>       bool use_pa;
> +     u32 eax, ebx, ecx, edx;
>  
>       if (IS_ENABLED(CONFIG_X86_32)) {
>               uci     = (struct ucode_cpu_info *)__pa_nodebug(ucode_cpu_info);
> @@ -315,7 +316,10 @@ void __init load_ucode_amd_bsp(unsigned int family)
>               return;
>  
>       /* Get BSP's CPUID.EAX(1), needed in load_microcode_amd() */
> -     uci->cpu_sig.sig = cpuid_eax(1);
> +     eax = 0x00000001;
> +     ecx = 0;
> +     native_cpuid(&eax, &ebx, &ecx, &edx);
> +     uci->cpu_sig.sig = eax;
>  
>       apply_microcode_early_amd(cp.data, cp.size, true);
>  }
> -- 

Applied, thanks.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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