Re: [PATCH v2 3/3] KVM: x86: #GP when attempts to write reserved bits of Variable Range MTRRs

Jan Kiszka
2014-08-29T16:52:46Z

On 2014-08-29 18:47, Paolo Bonzini wrote:
> Il 19/08/2014 11:04, Wanpeng Li ha scritto:
>> Section 11.11.2.3 of the SDM mentions "All other bits in the IA32_MTRR_PHYSBASEn
>> and IA32_MTRR_PHYSMASKn registers are reserved; the processor generates a
>> general-protection exception(#GP) if software attempts to write to them". This
>> patch do it in kvm.
>>
>> Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
>
> This breaks if the guest maxphyaddr is higher than the host's (which
> sometimes happens depending on your hardware and how QEMU is
> configured).
>
> You need to use cpuid_maxphyaddr, like this
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a375dfc42f6a..916e89515210 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1726,7 +1726,7 @@ static bool valid_mtrr_type(unsigned t)
> static bool mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> {
> int i;
> - u64 mask = 0;
> + u64 mask;
>
> if (!msr_mtrr_valid(msr))
> return false;
> @@ -1750,8 +1750,7 @@ static bool mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> /* variable MTRRs */
> WARN_ON(!(msr >= 0x200 && msr < 0x200 + 2 * KVM_NR_VAR_MTRR));
>
> - for (i = 63; i > boot_cpu_data.x86_phys_bits; i--)
> - mask |= (1ULL << i);
> + mask = (~0ULL) << cpuid_maxphyaddr(vcpu);
> if ((msr & 1) == 0) {
> /* MTRR base */
> if (!valid_mtrr_type(data & 0xff))
>
>
> Jan, can you see if this patch fixes the SeaBIOS triple fault you reported?

Yep, it does.

Jan

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