Advertise UMIP as emulated if and only if the host doesn't natively support UMIP, otherwise vmx_umip_emulated() is misleading when the host _does_ support UMIP. Of the four users of vmx_umip_emulated(), two already check for native support, and the logic in vmx_set_cpu_caps() is relevant if and only if UMIP isn't natively supported as UMIP is set in KVM's caps by kvm_set_cpu_caps() when UMIP is present in hardware. That leaves KVM's stuffing of X86_CR4_UMIP into the default cr4_fixed1 value enumerated for nested VMX. In that case, checking for (lack of) host support is actually a bug fix of sorts, as enumerating UMIP support based solely on descriptor table exiting works only because KVM doesn't sanity check MSR_IA32_VMX_CR4_FIXED1. E.g. if a (very theoretical) host supported UMIP in hardware but didn't allow UMIP+VMX, KVM would advertise UMIP but not actually emulate UMIP. Of course, KVM would explode long before it could run a nested VM on said theoretical CPU, as KVM doesn't modify host CR4 when enabling VMX, i.e. would load an "illegal" value into vmcs.HOST_CR4. Reported-by: Robert Hoo <robert.hu@xxxxxxxxx> Link: https://lore.kernel.org/all/20230310125718.1442088-2-robert.hu@xxxxxxxxx Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/vmx/capabilities.h | 4 ++-- arch/x86/kvm/vmx/nested.c | 3 +-- arch/x86/kvm/vmx/vmx.c | 2 +- 3 files changed, 4 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h index 45162c1bcd8f..d0abee35d7ba 100644 --- a/arch/x86/kvm/vmx/capabilities.h +++ b/arch/x86/kvm/vmx/capabilities.h @@ -152,8 +152,8 @@ static inline bool cpu_has_vmx_ept(void) static inline bool vmx_umip_emulated(void) { - return vmcs_config.cpu_based_2nd_exec_ctrl & - SECONDARY_EXEC_DESC; + return !boot_cpu_has(X86_FEATURE_UMIP) && + (vmcs_config.cpu_based_2nd_exec_ctrl & SECONDARY_EXEC_DESC); } static inline bool cpu_has_vmx_rdtscp(void) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 96ede74a6067..4fadf6c661d5 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -2328,8 +2328,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs0 * Preset *DT exiting when emulating UMIP, so that vmx_set_cr4() * will not have to rewrite the controls just for this bit. */ - if (!boot_cpu_has(X86_FEATURE_UMIP) && vmx_umip_emulated() && - (vmcs12->guest_cr4 & X86_CR4_UMIP)) + if (vmx_umip_emulated() && (vmcs12->guest_cr4 & X86_CR4_UMIP)) exec_control |= SECONDARY_EXEC_DESC; if (exec_control & SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 44fb619803b8..57464c762c79 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -3404,7 +3404,7 @@ void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4) else hw_cr4 |= KVM_PMODE_VM_CR4_ALWAYS_ON; - if (!boot_cpu_has(X86_FEATURE_UMIP) && vmx_umip_emulated()) { + if (vmx_umip_emulated()) { if (cr4 & X86_CR4_UMIP) { secondary_exec_controls_setbit(vmx, SECONDARY_EXEC_DESC); hw_cr4 &= ~X86_CR4_UMIP; -- 2.40.0.634.g4ca3ef3211-goog
