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KVM: x86: Use KVM-governed feature framework to track "XSAVES enabled" 

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.

Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/r/20230815203653.519297-7-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2023-08-15 13:36:44 -07:00
parent 662f681578
commit fe60e8f65f
5 changed files with 35 additions and 24 deletions
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1
arch/x86/include/asm/kvm_host.h
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@ -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;

1
arch/x86/kvm/governed_features.h
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@ -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

17
arch/x86/kvm/svm/svm.c
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@ -4244,9 +4244,20 @@ 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) &&

36
arch/x86/kvm/vmx/vmx.c
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@ -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);
@ -7743,10 +7744,9 @@ 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);

4
arch/x86/kvm/x86.c
View File

@ -1015,7 +1015,7 @@ 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);
}
@ -1046,7 +1046,7 @@ 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);
}