[PATCH v2 1/3] KVM: x86: Move some EFER bits enablement to common code

Yosry Ahmed
2026-03-07T01:16:29Z

Move EFER bits enablement that only depend on CPU support to common
code, as there is no reason to do it in vendor code. Leave EFER.SVME and
EFER.LMSLE enablement in SVM code as they depend on vendor module
parameters.

Having the enablement in common code ensures that if a vendor starts
supporting an existing feature, KVM doesn't end up advertising to
userspace but not allowing the EFER bit to be set.

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
---
arch/x86/kvm/svm/svm.c | 7 -------
arch/x86/kvm/vmx/vmx.c | 4 ----
arch/x86/kvm/x86.c | 14 ++++++++++++++
3 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 3407deac90bd6..5362443f4bbce 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5556,14 +5556,10 @@ static __init int svm_hardware_setup(void)
pr_err_ratelimited("NX (Execute Disable) not supported\n");
return -EOPNOTSUPP;
}
- kvm_enable_efer_bits(EFER_NX);

kvm_caps.supported_xcr0 &= ~(XFEATURE_MASK_BNDREGS |
XFEATURE_MASK_BNDCSR);

- if (boot_cpu_has(X86_FEATURE_FXSR_OPT))
- kvm_enable_efer_bits(EFER_FFXSR);
-
if (tsc_scaling) {
if (!boot_cpu_has(X86_FEATURE_TSCRATEMSR)) {
tsc_scaling = false;
@@ -5577,9 +5573,6 @@ static __init int svm_hardware_setup(void)

tsc_aux_uret_slot = kvm_add_user_return_msr(MSR_TSC_AUX);

- if (boot_cpu_has(X86_FEATURE_AUTOIBRS))
- kvm_enable_efer_bits(EFER_AUTOIBRS);
-
/* Check for pause filtering support */
if (!boot_cpu_has(X86_FEATURE_PAUSEFILTER)) {
pause_filter_count = 0;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9302c16571cdc..2b8a7456039c7 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8583,10 +8583,6 @@ __init int vmx_hardware_setup(void)

vmx_setup_user_return_msrs();

-
- if (boot_cpu_has(X86_FEATURE_NX))
- kvm_enable_efer_bits(EFER_NX);
-
if (boot_cpu_has(X86_FEATURE_MPX)) {
rdmsrq(MSR_IA32_BNDCFGS, host_bndcfgs);
WARN_ONCE(host_bndcfgs, "BNDCFGS in host will be lost");
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 879cdeb6adde2..1aae2bc380d1b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10025,6 +10025,18 @@ void kvm_setup_xss_caps(void)
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_setup_xss_caps);

+static void kvm_setup_efer_caps(void)
+{
+ if (boot_cpu_has(X86_FEATURE_NX))
+ kvm_enable_efer_bits(EFER_NX);
+
+ if (boot_cpu_has(X86_FEATURE_FXSR_OPT))
+ kvm_enable_efer_bits(EFER_FFXSR);
+
+ if (boot_cpu_has(X86_FEATURE_AUTOIBRS))
+ kvm_enable_efer_bits(EFER_AUTOIBRS);
+}
+
static inline void kvm_ops_update(struct kvm_x86_init_ops *ops)
{
memcpy(&kvm_x86_ops, ops->runtime_ops, sizeof(kvm_x86_ops));
@@ -10161,6 +10173,8 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
if (r != 0)
goto out_mmu_exit;

+ kvm_setup_efer_caps();
+
enable_device_posted_irqs &= enable_apicv &&
irq_remapping_cap(IRQ_POSTING_CAP);

--
2.53.0.473.g4a7958ca14-goog