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

Paolo

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