KVM: x86: Tweak name of MONITOR/MWAIT #UD quirk to make it #UD specific

Add a "UD" clause to KVM_X86_QUIRK_MWAIT_NEVER_FAULTS to make it clear
that the quirk only controls the #UD behavior of MONITOR/MWAIT.  KVM
doesn't currently enforce fault checks when MONITOR/MWAIT are supported,
but that could change in the future.  SVM also has a virtualization hole
in that it checks all faults before intercepts, and so "never faults" is
already a lie when running on SVM.

Fixes: bfbcc81 ("KVM: x86: Add a quirk for KVM's "MONITOR/MWAIT are NOPs!" behavior")
Signed-off-by: Sean Christopherson <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: sean-jc

Documentation/virt/kvm/api.rst

@@ -7523,7 +7523,7 @@ The valid bits in cap.args[0] are:
                                     incorrect hypercall instruction will
                                     generate a #UD within the guest.
 
-KVM_X86_QUIRK_MWAIT_NEVER_FAULTS    By default, KVM emulates MONITOR/MWAIT (if
+KVM_X86_QUIRK_MWAIT_NEVER_UD_FAULTS By default, KVM emulates MONITOR/MWAIT (if
                                     they are intercepted) as NOPs regardless of
                                     whether or not MONITOR/MWAIT are supported
                                     according to guest CPUID.  When this quirk

arch/x86/include/asm/kvm_host.h

@@ -2096,6 +2096,6 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
 	 KVM_X86_QUIRK_OUT_7E_INC_RIP |		\
 	 KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT |	\
 	 KVM_X86_QUIRK_FIX_HYPERCALL_INSN |	\
-	 KVM_X86_QUIRK_MWAIT_NEVER_FAULTS)
+	 KVM_X86_QUIRK_MWAIT_NEVER_UD_FAULTS)
 
 #endif /* _ASM_X86_KVM_HOST_H */

arch/x86/include/uapi/asm/kvm.h

@@ -439,7 +439,7 @@ struct kvm_sync_regs {
 #define KVM_X86_QUIRK_OUT_7E_INC_RIP		(1 << 3)
 #define KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT	(1 << 4)
 #define KVM_X86_QUIRK_FIX_HYPERCALL_INSN	(1 << 5)
-#define KVM_X86_QUIRK_MWAIT_NEVER_FAULTS	(1 << 6)
+#define KVM_X86_QUIRK_MWAIT_NEVER_UD_FAULTS	(1 << 6)
 
 #define KVM_STATE_NESTED_FORMAT_VMX	0
 #define KVM_STATE_NESTED_FORMAT_SVM	1

arch/x86/kvm/x86.c

@@ -2046,7 +2046,7 @@ EXPORT_SYMBOL_GPL(kvm_handle_invalid_op);
 
 static int kvm_emulate_monitor_mwait(struct kvm_vcpu *vcpu, const char *insn)
 {
-	if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MWAIT_NEVER_FAULTS) &&
+	if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MWAIT_NEVER_UD_FAULTS) &&
 	    !guest_cpuid_has(vcpu, X86_FEATURE_MWAIT))
 		return kvm_handle_invalid_op(vcpu);
 

tools/testing/selftests/kvm/x86_64/monitor_mwait_test.c

@@ -113,7 +113,7 @@ int main(int argc, char *argv[])
 
 		disabled_quirks = 0;
 		if (testcase & MWAIT_QUIRK_DISABLED)
-			disabled_quirks |= KVM_X86_QUIRK_MWAIT_NEVER_FAULTS;
+			disabled_quirks |= KVM_X86_QUIRK_MWAIT_NEVER_UD_FAULTS;
 		if (testcase & MISC_ENABLES_QUIRK_DISABLED)
 			disabled_quirks |= KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT;
 		vm_enable_cap(vm, KVM_CAP_DISABLE_QUIRKS2, disabled_quirks);