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

[Paolo Bonzini]

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.mo...@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