[PATCH v3 06/15] KVM: x86: Use KVM-governed feature framework to track "XSAVES enabled"
From: Sean Christopherson
Date: Tue Aug 15 2023 - 16:38:54 EST
Use the governed feature framework to track if XSAVES is "enabled", i.e.
if XSAVES can be used by the guest. Add a comment in the SVM code to
explain the very unintuitive logic of deliberately NOT checking if XSAVES
is enumerated in the guest CPUID model.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 -
arch/x86/kvm/governed_features.h | 1 +
arch/x86/kvm/svm/svm.c | 17 ++++++++++++---
arch/x86/kvm/vmx/vmx.c | 36 ++++++++++++++++----------------
arch/x86/kvm/x86.c | 4 ++--
5 files changed, 35 insertions(+), 24 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 60d430b4650f..9f57aa33798b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -746,7 +746,6 @@ struct kvm_vcpu_arch {
u64 smi_count;
bool at_instruction_boundary;
bool tpr_access_reporting;
- bool xsaves_enabled;
bool xfd_no_write_intercept;
u64 ia32_xss;
u64 microcode_version;
diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
index b29c15d5e038..b896a64e4ac3 100644
--- a/arch/x86/kvm/governed_features.h
+++ b/arch/x86/kvm/governed_features.h
@@ -6,6 +6,7 @@ BUILD_BUG()
#define KVM_GOVERNED_X86_FEATURE(x) KVM_GOVERNED_FEATURE(X86_FEATURE_##x)
KVM_GOVERNED_X86_FEATURE(GBPAGES)
+KVM_GOVERNED_X86_FEATURE(XSAVES)
#undef KVM_GOVERNED_X86_FEATURE
#undef KVM_GOVERNED_FEATURE
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 6aaa3c7b4578..d67f6e23dcd2 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4273,9 +4273,20 @@ 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) &&
- boot_cpu_has(X86_FEATURE_XSAVES);
+ /*
+ * SVM doesn't provide a way to disable just XSAVES in the guest, KVM
+ * can only disable all variants of by disallowing CR4.OSXSAVE from
+ * being set. As a result, if the host has XSAVE and XSAVES, and the
+ * guest has XSAVE enabled, the guest can execute XSAVES without
+ * faulting. Treat XSAVES as enabled in this case regardless of
+ * whether it's advertised to the guest so that KVM context switches
+ * XSS on VM-Enter/VM-Exit. Failure to do so would effectively give
+ * the guest read/write access to the host's XSS.
+ */
+ if (boot_cpu_has(X86_FEATURE_XSAVE) &&
+ boot_cpu_has(X86_FEATURE_XSAVES) &&
+ guest_cpuid_has(vcpu, X86_FEATURE_XSAVE))
+ kvm_governed_feature_set(vcpu, X86_FEATURE_XSAVES);
/* Update nrips enabled cache */
svm->nrips_enabled = kvm_cpu_cap_has(X86_FEATURE_NRIPS) &&
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 22975cc949b7..6314ca32a5cf 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4543,16 +4543,19 @@ vmx_adjust_secondary_exec_control(struct vcpu_vmx *vmx, u32 *exec_control,
* based on a single guest CPUID bit, with a dedicated feature bit. This also
* verifies that the control is actually supported by KVM and hardware.
*/
-#define vmx_adjust_sec_exec_control(vmx, exec_control, name, feat_name, ctrl_name, exiting) \
-({ \
- bool __enabled; \
- \
- if (cpu_has_vmx_##name()) { \
- __enabled = guest_cpuid_has(&(vmx)->vcpu, \
- X86_FEATURE_##feat_name); \
- vmx_adjust_secondary_exec_control(vmx, exec_control, \
- SECONDARY_EXEC_##ctrl_name, __enabled, exiting); \
- } \
+#define vmx_adjust_sec_exec_control(vmx, exec_control, name, feat_name, ctrl_name, exiting) \
+({ \
+ struct kvm_vcpu *__vcpu = &(vmx)->vcpu; \
+ bool __enabled; \
+ \
+ if (cpu_has_vmx_##name()) { \
+ if (kvm_is_governed_feature(X86_FEATURE_##feat_name)) \
+ __enabled = guest_can_use(__vcpu, X86_FEATURE_##feat_name); \
+ else \
+ __enabled = guest_cpuid_has(__vcpu, X86_FEATURE_##feat_name); \
+ vmx_adjust_secondary_exec_control(vmx, exec_control, SECONDARY_EXEC_##ctrl_name,\
+ __enabled, exiting); \
+ } \
})
/* More macro magic for ENABLE_/opt-in versus _EXITING/opt-out controls. */
@@ -4612,10 +4615,7 @@ static u32 vmx_secondary_exec_control(struct vcpu_vmx *vmx)
if (!enable_pml || !atomic_read(&vcpu->kvm->nr_memslots_dirty_logging))
exec_control &= ~SECONDARY_EXEC_ENABLE_PML;
- if (cpu_has_vmx_xsaves())
- vmx_adjust_secondary_exec_control(vmx, &exec_control,
- SECONDARY_EXEC_ENABLE_XSAVES,
- vcpu->arch.xsaves_enabled, false);
+ vmx_adjust_sec_exec_feature(vmx, &exec_control, xsaves, XSAVES);
/*
* RDPID is also gated by ENABLE_RDTSCP, turn on the control if either
@@ -4634,6 +4634,7 @@ static u32 vmx_secondary_exec_control(struct vcpu_vmx *vmx)
SECONDARY_EXEC_ENABLE_RDTSCP,
rdpid_or_rdtscp_enabled, false);
}
+
vmx_adjust_sec_exec_feature(vmx, &exec_control, invpcid, INVPCID);
vmx_adjust_sec_exec_exiting(vmx, &exec_control, rdrand, RDRAND);
@@ -7745,10 +7746,9 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
* to the guest. XSAVES depends on CR4.OSXSAVE, and CR4.OSXSAVE can be
* set if and only if XSAVE is supported.
*/
- vcpu->arch.xsaves_enabled = kvm_cpu_cap_has(X86_FEATURE_XSAVES) &&
- boot_cpu_has(X86_FEATURE_XSAVE) &&
- guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) &&
- guest_cpuid_has(vcpu, X86_FEATURE_XSAVES);
+ if (boot_cpu_has(X86_FEATURE_XSAVE) &&
+ guest_cpuid_has(vcpu, X86_FEATURE_XSAVE))
+ kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_XSAVES);
vmx_setup_uret_msrs(vmx);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index eba35d43e3fe..34945c7dba38 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1016,7 +1016,7 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
if (vcpu->arch.xcr0 != host_xcr0)
xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
- if (vcpu->arch.xsaves_enabled &&
+ if (guest_can_use(vcpu, X86_FEATURE_XSAVES) &&
vcpu->arch.ia32_xss != host_xss)
wrmsrl(MSR_IA32_XSS, vcpu->arch.ia32_xss);
}
@@ -1047,7 +1047,7 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
if (vcpu->arch.xcr0 != host_xcr0)
xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
- if (vcpu->arch.xsaves_enabled &&
+ if (guest_can_use(vcpu, X86_FEATURE_XSAVES) &&
vcpu->arch.ia32_xss != host_xss)
wrmsrl(MSR_IA32_XSS, host_xss);
}
--
2.41.0.694.ge786442a9b-goog