[1/2] KVM: VMX: Treat UMIP as emulated if and only if the host doesn't have UMIP
Commit Message
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@intel.com>
Link: https://lore.kernel.org/all/20230310125718.1442088-2-robert.hu@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
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(-)
@@ -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)
@@ -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)
@@ -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;