Re: [PATCH v2 2/2] KVM: CPUID: Put maxphyaddr updating together with virtual address width checking

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On Tue, Sep 10, 2019 at 3:42 AM Xiaoyao Li <xiaoyao.li@xxxxxxxxx> wrote:
>
> Since both of maxphyaddr updating and virtual address width checking
> need to query the cpuid leaf 0x80000008. We can put them together.
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> ---
>  arch/x86/kvm/cpuid.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 67fa44ab87af..fd0a66079001 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -118,6 +118,7 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>                 best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
>
>         /*
> +        * Update physical address width and check virtual address width.
>          * The existing code assumes virtual address is 48-bit or 57-bit in the
>          * canonical address checks; exit if it is ever changed.
>          */
> @@ -127,7 +128,10 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>
>                 if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
>                         return -EINVAL;
> +
> +               vcpu->arch.maxphyaddr = best->eax & 0xff;
>         }
> +       vcpu->arch.maxphyaddr = 36;

Perhaps I'm missing something, but it looks to me like you always set
vcpu->arch.maxphyaddr to 36, regardless of what may be enumerated by
leaf 0x80000008.

Is there really much of an advantage to open-coding
cpuid_query_maxphyaddr() here?

>         best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
>         if (kvm_hlt_in_guest(vcpu->kvm) && best &&
> @@ -144,8 +148,6 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>                 }
>         }
>
> -       /* Update physical-address width */
> -       vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
>         kvm_mmu_reset_context(vcpu);
>
>         kvm_pmu_refresh(vcpu);
> --
> 2.19.1
>



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