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    SubjectRe: [PATCH v2] KVM: x86: use CPUID to locate host page table reserved bits
    On Wed, Dec 04, 2019 at 04:40:37PM +0100, Paolo Bonzini wrote:
    > The comment in kvm_get_shadow_phys_bits refers to MKTME, but the same is actually
    > true of SME and SEV. Just use CPUID[0x8000_0008].EAX[7:0] unconditionally if
    > available, it is simplest and works even if memory is not encrypted.
    >
    > Cc: stable@vger.kernel.org
    > Reported-by: Tom Lendacky <thomas.lendacky@amd.com>
    > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    > ---
    > arch/x86/kvm/mmu/mmu.c | 20 ++++++++++++--------
    > 1 file changed, 12 insertions(+), 8 deletions(-)
    >
    > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
    > index 6f92b40d798c..1e4ee4f8de5f 100644
    > --- a/arch/x86/kvm/mmu/mmu.c
    > +++ b/arch/x86/kvm/mmu/mmu.c
    > @@ -538,16 +538,20 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
    > static u8 kvm_get_shadow_phys_bits(void)
    > {
    > /*
    > - * boot_cpu_data.x86_phys_bits is reduced when MKTME is detected
    > - * in CPU detection code, but MKTME treats those reduced bits as
    > - * 'keyID' thus they are not reserved bits. Therefore for MKTME
    > - * we should still return physical address bits reported by CPUID.
    > + * boot_cpu_data.x86_phys_bits is reduced when MKTME or SME are detected
    > + * in CPU detection code, but the processor treats those reduced bits as
    > + * 'keyID' thus they are not reserved bits. Therefore KVM needs to look at
    > + * the physical address bits reported by CPUID.
    > */
    > - if (!boot_cpu_has(X86_FEATURE_TME) ||
    > - WARN_ON_ONCE(boot_cpu_data.extended_cpuid_level < 0x80000008))
    > - return boot_cpu_data.x86_phys_bits;
    > + if (likely(boot_cpu_data.extended_cpuid_level >= 0x80000008))
    > + return cpuid_eax(0x80000008) & 0xff;
    >
    > - return cpuid_eax(0x80000008) & 0xff;
    > + /*
    > + * Quite weird to have VMX or SVM but not MAXPHYADDR; probably a VM with
    > + * custom CPUID. Proceed with whatever the kernel found since these features
    > + * aren't virtualizable (SME/SEV also require CPUIDs higher than 0x80000008).

    No love for MKTME? :-D

    Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>

    > + */
    > + return boot_cpu_data.x86_phys_bits;
    > }
    >
    > static void kvm_mmu_reset_all_pte_masks(void)
    > --
    > 1.8.3.1
    >

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