[PATCH v5 05/15] KVM: SEV: Mask CPUID[0x8000001F].eax according to supported features

Sean Christopherson
2021-04-22T02:11:49Z

From: Paolo Bonzini <pbonzini@redhat.com>

Add a reverse-CPUID entry for the memory encryption word, 0x8000001F.EAX,
and use it to override the supported CPUID flags reported to userspace.
Masking the reported CPUID flags avoids over-reporting KVM support, e.g.
without the mask a SEV-SNP capable CPU may incorrectly advertise SNP
support to userspace.

Clear SEV/SEV-ES if their corresponding module parameters are disabled,
and clear the memory encryption leaf completely if SEV is not fully
supported in KVM. Advertise SME_COHERENT in addition to SEV and SEV-ES,
as the guest can use SME_COHERENT to avoid CLFLUSH operations.

Explicitly omit SME and VM_PAGE_FLUSH from the reporting. These features
are used by KVM, but are not exposed to the guest, e.g. guest access to
related MSRs will fault.

Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/cpuid.c | 8 +++++++-
arch/x86/kvm/cpuid.h | 1 +
arch/x86/kvm/svm/sev.c | 8 ++++++++
arch/x86/kvm/svm/svm.c | 3 +++
arch/x86/kvm/svm/svm.h | 1 +
5 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 2ae061586677..96e41e1a1bde 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -557,6 +557,10 @@ void kvm_set_cpu_caps(void)
*/
kvm_cpu_cap_mask(CPUID_8000_000A_EDX, 0);

+ kvm_cpu_cap_mask(CPUID_8000_001F_EAX,
+ 0 /* SME */ | F(SEV) | 0 /* VM_PAGE_FLUSH */ | F(SEV_ES) |
+ F(SME_COHERENT));
+
kvm_cpu_cap_mask(CPUID_C000_0001_EDX,
F(XSTORE) | F(XSTORE_EN) | F(XCRYPT) | F(XCRYPT_EN) |
F(ACE2) | F(ACE2_EN) | F(PHE) | F(PHE_EN) |
@@ -944,8 +948,10 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
break;
/* Support memory encryption cpuid if host supports it */
case 0x8000001F:
- if (!boot_cpu_has(X86_FEATURE_SEV))
+ if (!kvm_cpu_cap_has(X86_FEATURE_SEV))
entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+ else
+ cpuid_entry_override(entry, CPUID_8000_001F_EAX);
break;
/*Add support for Centaur's CPUID instruction*/
case 0xC0000000:
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 888e88b42e8d..eeb4a3020e1b 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -99,6 +99,7 @@ static const struct cpuid_reg reverse_cpuid[] = {
[CPUID_7_EDX] = { 7, 0, CPUID_EDX},
[CPUID_7_1_EAX] = { 7, 1, CPUID_EAX},
[CPUID_12_EAX] = {0x00000012, 0, CPUID_EAX},
+ [CPUID_8000_001F_EAX] = {0x8000001f, 0, CPUID_EAX},
};

/*
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index fb32b93e325c..e54eff6dfbbe 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1764,6 +1764,14 @@ void sev_vm_destroy(struct kvm *kvm)
sev_asid_free(sev->asid);
}

+void __init sev_set_cpu_caps(void)
+{
+ if (!sev)
+ kvm_cpu_cap_clear(X86_FEATURE_SEV);
+ if (!sev_es)
+ kvm_cpu_cap_clear(X86_FEATURE_SEV_ES);
+}
+
void __init sev_hardware_setup(void)
{
unsigned int eax, ebx, ecx, edx;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 12b2c04076bb..cb227e90dffb 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -914,6 +914,9 @@ static __init void svm_set_cpu_caps(void)
if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) ||
boot_cpu_has(X86_FEATURE_AMD_SSBD))
kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
+
+ /* CPUID 0x8000001F (SME/SEV features) */
+ sev_set_cpu_caps();
}

static __init int svm_hardware_setup(void)
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index ec0407f41458..39d1412f2c45 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -581,6 +581,7 @@ int svm_unregister_enc_region(struct kvm *kvm,
struct kvm_enc_region *range);
int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd);
void pre_sev_run(struct vcpu_svm *svm, int cpu);
+void __init sev_set_cpu_caps(void);
void __init sev_hardware_setup(void);
void sev_hardware_teardown(void);
void sev_free_vcpu(struct kvm_vcpu *vcpu);