Re: [Qemu-devel] [PATCH 2/4] KVM/X86: Fix xsave cpuid exposing bug

[Paolo Bonzini]

Il 02/12/2013 17:45, Liu, Jinsong ha scritto:
> From 4a2eb0a8467b4f278e59d2df209a1bc03349d088 Mon Sep 17 00:00:00 2001
> From: Liu Jinsong <address@hidden>
> Date: Tue, 3 Dec 2013 06:28:20 +0800
> Subject: [PATCH 2/4] KVM/X86: Fix xsave cpuid exposing bug
> 
> EBX of cpuid(0xD, 0) is dynamic per XCR0 features enable/disable.
> Bit 63 of XCR0 is reserved for future expansion.
> 
> Signed-off-by: Liu Jinsong <address@hidden>
> ---
>  arch/x86/include/asm/xsave.h |    2 ++
>  arch/x86/kvm/cpuid.c         |    6 +++---
>  arch/x86/kvm/x86.c           |    7 +++++--
>  3 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
> index d3e3ea5..6120e74 100644
> --- a/arch/x86/include/asm/xsave.h
> +++ b/arch/x86/include/asm/xsave.h
> @@ -13,6 +13,8 @@
>  #define XSTATE_BNDCSR        0x10
>  
>  #define XSTATE_FPSSE (XSTATE_FP | XSTATE_SSE)
> +/* Bit 63 of XCR0 is reserved for future expansion */
> +#define XSTATE_EXTEND_MASK   (~(XSTATE_FPSSE | (1 << 63)))
>  
>  #define FXSAVE_SIZE  512
>  

This hunk also needs an Acked-by from the x86 maintainers.

> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index c697625..2d661e6 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -28,7 +28,7 @@ static u32 xstate_required_size(u64 xstate_bv)
>       int feature_bit = 0;
>       u32 ret = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;
>  
> -     xstate_bv &= ~XSTATE_FPSSE;
> +     xstate_bv &= XSTATE_EXTEND_MASK;
>       while (xstate_bv) {
>               if (xstate_bv & 0x1) {
>                       u32 eax, ebx, ecx, edx;
> @@ -74,8 +74,8 @@ void kvm_update_cpuid(struct kvm_vcpu *vcpu)
>               vcpu->arch.guest_supported_xcr0 =
>                       (best->eax | ((u64)best->edx << 32)) &
>                       host_xcr0 & KVM_SUPPORTED_XCR0;
> -             vcpu->arch.guest_xstate_size =
> -                     xstate_required_size(vcpu->arch.guest_supported_xcr0);
> +             vcpu->arch.guest_xstate_size = best->ebx =
> +                     xstate_required_size(vcpu->arch.xcr0);
>       }
>  
>       kvm_pmu_cpuid_update(vcpu);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 21ef1ba..1657ca2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -576,13 +576,13 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
>  
>  int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
>  {
> -     u64 xcr0;
> +     u64 xcr0 = xcr;
> +     u64 old_xcr0 = vcpu->arch.xcr0;
>       u64 valid_bits;
>  
>       /* Only support XCR_XFEATURE_ENABLED_MASK(xcr0) now  */
>       if (index != XCR_XFEATURE_ENABLED_MASK)
>               return 1;
> -     xcr0 = xcr;
>       if (!(xcr0 & XSTATE_FP))
>               return 1;
>       if ((xcr0 & XSTATE_YMM) && !(xcr0 & XSTATE_SSE))
> @@ -599,6 +599,9 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 
> xcr)
>  
>       kvm_put_guest_xcr0(vcpu);
>       vcpu->arch.xcr0 = xcr0;
> +
> +     if ((xcr0 ^ old_xcr0) & XSTATE_EXTEND_MASK)
> +             kvm_update_cpuid(vcpu);
>       return 0;
>  }
>  
> -- 1.7.1