Re: [PATCH 2/2] KVM:SVM: Mask SEV encryption bit from CR3 reserved bits

[Babu Moger <babu.moger@amd.com>]

On 11/12/20 2:32 AM, Paolo Bonzini wrote:
> On 12/11/20 01:28, Babu Moger wrote:
>> Add support to the mask_cr3_rsvd_bits() callback to mask the
>> encryption bit from the CR3 value when SEV is enabled.
>>
>> Additionally, cache the encryption mask for quick access during
>> the check.
>>
>> Fixes: a780a3ea628268b2 ("KVM: X86: Fix reserved bits check for MOV to
>> CR3")
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
>>   arch/x86/kvm/svm/svm.c |   11 ++++++++++-
>>   arch/x86/kvm/svm/svm.h |    3 +++
>>   2 files changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index a491a47d7f5c..c2b1e52810c6 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -3741,6 +3741,7 @@ static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu,
>> gfn_t gfn, bool is_mmio)
>>   static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>>   {
>>       struct vcpu_svm *svm = to_svm(vcpu);
>> +    struct kvm_cpuid_entry2 *best;
>>         vcpu->arch.xsaves_enabled = guest_cpuid_has(vcpu,
>> X86_FEATURE_XSAVE) &&
>>                       boot_cpu_has(X86_FEATURE_XSAVE) &&
>> @@ -3771,6 +3772,12 @@ static void svm_vcpu_after_set_cpuid(struct
>> kvm_vcpu *vcpu)
>>       if (nested && guest_cpuid_has(vcpu, X86_FEATURE_SVM))
>>           kvm_request_apicv_update(vcpu->kvm, false,
>>                        APICV_INHIBIT_REASON_NESTED);
>> +
>> +    best = kvm_find_cpuid_entry(vcpu, 0x8000001F, 0);
>> +    if (best)
>> +        svm->sev_enc_mask = ~(1UL << (best->ebx & 0x3f));
>> +    else
>> +        svm->sev_enc_mask = ~0UL;
>>   }
>>     static bool svm_has_wbinvd_exit(void)
>> @@ -4072,7 +4079,9 @@ static void enable_smi_window(struct kvm_vcpu *vcpu)
>>     static unsigned long svm_mask_cr3_rsvd_bits(struct kvm_vcpu *vcpu,
>> unsigned long cr3)
>>   {
>> -    return cr3;
>> +    struct vcpu_svm *svm = to_svm(vcpu);
>> +
>> +    return sev_guest(vcpu->kvm) ? (cr3 & svm->sev_enc_mask) : cr3;
>>   }
>>     static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, void
>> *insn, int insn_len)
>> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
>> index 1d853fe4c778..57a36645a0e4 100644
>> --- a/arch/x86/kvm/svm/svm.h
>> +++ b/arch/x86/kvm/svm/svm.h
>> @@ -152,6 +152,9 @@ struct vcpu_svm {
>>       u64 *avic_physical_id_cache;
>>       bool avic_is_running;
>>   +    /* SEV Memory encryption mask */
>> +    unsigned long sev_enc_mask;
>> +
>>       /*
>>        * Per-vcpu list of struct amd_svm_iommu_ir:
>>        * This is used mainly to store interrupt remapping information used
>>
> 
> Instead of adding a new callback, you can add a field to struct
> kvm_vcpu_arch:
> 
>      if (is_long_mode(vcpu) &&
> -        (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 63)))
> +        (cr3 & vcpu->arch.cr3_lm_rsvd_bits))
> 
> Set it in kvm_vcpu_after_set_cpuid, and clear the memory encryption bit in
> kvm_x86_ops.vcpu_after_set_cpuid.

Yes. That should work. Will resubmit the patches. Thanks