[PATCH v2 64/66] KVM: nSVM: Expose SVM features to L1 iff nested is enabled

Sean Christopherson
2020-03-02T23:59:23Z

Set SVM feature bits in KVM capabilities if and only if nested=true, KVM
shouldn't advertise features that realistically can't be used. Use
kvm_cpu_cap_has(X86_FEATURE_SVM) to indirectly query "nested" in
svm_set_supported_cpuid() in anticipation of moving CPUID 0x8000000A
adjustments into common x86 code.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/svm.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index f32fc3c03667..8e39dcd3160d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1373,21 +1373,21 @@ static __init void svm_set_cpu_caps(void)
if (avic)
kvm_cpu_cap_clear(X86_FEATURE_X2APIC);

- /* CPUID 0x80000001 */
- if (nested)
+ /* CPUID 0x80000001 and 0x8000000A (SVM features) */
+ if (nested) {
kvm_cpu_cap_set(X86_FEATURE_SVM);

+ if (boot_cpu_has(X86_FEATURE_NRIPS))
+ kvm_cpu_cap_set(X86_FEATURE_NRIPS);
+
+ if (npt_enabled)
+ kvm_cpu_cap_set(X86_FEATURE_NPT);
+ }
+
/* CPUID 0x80000008 */
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 0x8000000A */
- /* Support next_rip if host supports it */
- kvm_cpu_cap_check_and_set(X86_FEATURE_NRIPS);
-
- if (npt_enabled)
- kvm_cpu_cap_set(X86_FEATURE_NPT);
}

static __init int svm_hardware_setup(void)
@@ -6051,6 +6051,10 @@ static void svm_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
{
switch (entry->function) {
case 0x8000000A:
+ if (!kvm_cpu_cap_has(X86_FEATURE_SVM)) {
+ entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+ break;
+ }
entry->eax = 1; /* SVM revision 1 */
entry->ebx = 8; /* Lets support 8 ASIDs in case we add proper
ASID emulation to nested SVM */
--
2.24.1