From bfbcc81bb82cbbad8bf4e40cea274f42b50674e2 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 8 Jun 2022 22:45:12 +0000 Subject: KVM: x86: Add a quirk for KVM's "MONITOR/MWAIT are NOPs!" behavior Add a quirk for KVM's behavior of emulating intercepted MONITOR/MWAIT instructions a NOPs regardless of whether or not they are supported in guest CPUID. KVM's current behavior was likely motiviated by a certain fruity operating system that expects MONITOR/MWAIT to be supported unconditionally and blindly executes MONITOR/MWAIT without first checking CPUID. And because KVM does NOT advertise MONITOR/MWAIT to userspace, that's effectively the default setup for any VMM that regurgitates KVM_GET_SUPPORTED_CPUID to KVM_SET_CPUID2. Note, this quirk interacts with KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT. The behavior is actually desirable, as userspace VMMs that want to unconditionally hide MONITOR/MWAIT from the guest can leave the MISC_ENABLE quirk enabled. Signed-off-by: Sean Christopherson Message-Id: <20220608224516.3788274-2-seanjc@google.com> Signed-off-by: Paolo Bonzini --- Documentation/virt/kvm/api.rst | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'Documentation/virt') diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 84c486ce6279..320cb04f7bd9 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7522,6 +7522,19 @@ The valid bits in cap.args[0] are: hypercall instructions. Executing the incorrect hypercall instruction will generate a #UD within the guest. + +KVM_X86_QUIRK_MWAIT_NEVER_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 + is disabled and KVM_X86_DISABLE_EXITS_MWAIT + is not set (MONITOR/MWAIT are intercepted), + KVM will inject a #UD on MONITOR/MWAIT if + they're unsupported per guest CPUID. Note, + KVM will modify MONITOR/MWAIT support in + guest CPUID on writes to MISC_ENABLE if + KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT is + disabled. =================================== ============================================ 7.32 KVM_CAP_MAX_VCPU_ID -- cgit v1.2.3