[PATCH Part2 RFC v3 29/37] KVM: SVM: Add support to handle GHCB GPA register VMGEXIT

Brijesh Singh
2021-06-02T14:17:15Z

SEV-SNP guests are required to perform a GHCB GPA registration (see
section 2.5.2 in GHCB specification). Before using a GHCB GPA for a vCPU
the first time, a guest must register the vCPU GHCB GPA. If hypervisor
can work with the guest requested GPA then it must respond back with the
same GPA otherwise return -1.

On VMEXIT, Verify that GHCB GPA matches with the registered value. If a
mismatch is detected then abort the guest.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
arch/x86/include/asm/sev-common.h | 1 +
arch/x86/kvm/svm/sev.c | 25 +++++++++++++++++++++++++
arch/x86/kvm/svm/svm.h | 7 +++++++
3 files changed, 33 insertions(+)

diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 97137f1a567b..e7c6ce2ce45e 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -93,6 +93,7 @@
GHCB_MSR_GPA_REG_REQ)

#define GHCB_MSR_GPA_REG_RESP 0x013
+#define GHCB_MSR_GPA_REG_ERROR GENMASK_ULL(51, 0)
#define GHCB_MSR_GPA_REG_RESP_VAL(v) ((v) >> GHCB_MSR_GPA_REG_VALUE_POS)

/* SNP Page State Change NAE event */
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 6b0c230c5f37..81c0fc883261 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2900,6 +2900,25 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
GHCB_MSR_INFO_MASK, GHCB_MSR_INFO_POS);
break;
}
+ case GHCB_MSR_GPA_REG_REQ: {
+ kvm_pfn_t pfn;
+ u64 gfn;
+
+ gfn = get_ghcb_msr_bits(svm, GHCB_MSR_GPA_REG_GFN_MASK,
+ GHCB_MSR_GPA_REG_VALUE_POS);
+
+ pfn = kvm_vcpu_gfn_to_pfn(vcpu, gfn);
+ if (is_error_noslot_pfn(pfn))
+ gfn = GHCB_MSR_GPA_REG_ERROR;
+ else
+ svm->ghcb_registered_gpa = gfn_to_gpa(gfn);
+
+ set_ghcb_msr_bits(svm, gfn, GHCB_MSR_GPA_REG_GFN_MASK,
+ GHCB_MSR_GPA_REG_VALUE_POS);
+ set_ghcb_msr_bits(svm, GHCB_MSR_GPA_REG_RESP, GHCB_MSR_INFO_MASK,
+ GHCB_MSR_INFO_POS);
+ break;
+ }
case GHCB_MSR_TERM_REQ: {
u64 reason_set, reason_code;

@@ -2948,6 +2967,12 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
return -EINVAL;
}

+ /* SEV-SNP guest requires that the GHCB GPA must be registered */
+ if (sev_snp_guest(svm->vcpu.kvm) && !ghcb_gpa_is_registered(svm, ghcb_gpa)) {
+ vcpu_unimpl(&svm->vcpu, "vmgexit: GHCB GPA [%#llx] is not registered.\n", ghcb_gpa);
+ return -EINVAL;
+ }
+
svm->ghcb = svm->ghcb_map.hva;
ghcb = svm->ghcb_map.hva;

diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 32abcbd774d0..af4cce39b30f 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -185,6 +185,8 @@ struct vcpu_svm {
bool ghcb_sa_free;

bool guest_state_loaded;
+
+ u64 ghcb_registered_gpa;
};

struct svm_cpu_data {
@@ -245,6 +247,11 @@ static inline bool sev_snp_guest(struct kvm *kvm)
#endif
}

+static inline bool ghcb_gpa_is_registered(struct vcpu_svm *svm, u64 val)
+{
+ return svm->ghcb_registered_gpa == val;
+}
+
static inline void vmcb_mark_all_dirty(struct vmcb *vmcb)
{
vmcb->control.clean = 0;
--
2.17.1