Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

Konrad Rzeszutek Wilk
2014-12-01T22:11:36Z

On Mon, Dec 01, 2014 at 04:27:44PM -0500, Boris Ostrovsky wrote:
> Paravirtual guests are not expected to load microcode into processors
> and therefore it is not necessary to initialize microcode loading
> logic.

CC-ing the KVM folks since they use the paravirt interface too.
>
> In fact, under certain circumstances initializing this logic may cause
> the guest to crash. Specifically, 32-bit kernels use __pa_nodebug()
> macro which does not work in Xen (the code path that leads to this macro
> happens during resume when we call mc_bp_resume()->load_ucode_ap()
> ->check_loader_disabled_ap())
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> ---
> arch/x86/kernel/cpu/microcode/core.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> index 2ce9051..ebd232d 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -557,7 +557,7 @@ static int __init microcode_init(void)
> struct cpuinfo_x86 *c = &cpu_data(0);
> int error;
>
> - if (dis_ucode_ldr)
> + if (paravirt_enabled() || dis_ucode_ldr)
> return 0;
>
> if (c->x86_vendor == X86_VENDOR_INTEL)
> --
> 1.7.1
>