Use kvm_is_cr4_bit_set() to read guest CR4.UMIP when sanity checking that a descriptor table VM-Exit occurs if and only if guest.CR4.UMIP=1. UMIP can't be guest-owned, i.e. using kvm_read_cr4_bits() to decache guest- owned bits isn't strictly necessary, but eliminating raw reads of vcpu->arch.cr4 is desirable as it makes it easy to visually audit KVM for correctness. Opportunistically add a compile-time assertion that UMIP isn't guest-owned as letting the guest own UMIP isn't compatible with emulation (or any CR4 bit that is emulated by KVM). Opportunistically change the WARN_ON() to a ONCE variant. When the WARN fires, it fires _a lot_, and spamming the kernel logs ends up doing more harm than whatever led to KVM's unnecessary emulation. Reported-by: Robert Hoo <robert.hu@xxxxxxxxx> Link: https://lore.kernel.org/all/20230310125718.1442088-4-robert.hu@xxxxxxxxx Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/vmx/vmx.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 57464c762c79..f0975e790f7f 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -5402,7 +5402,13 @@ static int handle_set_cr4(struct kvm_vcpu *vcpu, unsigned long val) static int handle_desc(struct kvm_vcpu *vcpu) { - WARN_ON(!(vcpu->arch.cr4 & X86_CR4_UMIP)); + /* + * UMIP emulation relies on intercepting writes to CR4.UMIP, i.e. this + * and other code needs to be updated if UMIP can be guest owned. + */ + BUILD_BUG_ON(KVM_POSSIBLE_CR4_GUEST_BITS & X86_CR4_UMIP); + + WARN_ON_ONCE(!kvm_is_cr4_bit_set(vcpu, X86_CR4_UMIP)); return kvm_emulate_instruction(vcpu, 0); } -- 2.40.0.634.g4ca3ef3211-goog
