On Tue, Aug 13, 2024, Sean Christopherson wrote: > On Fri, May 31, 2024, Chao Gao wrote: > > On Thu, May 30, 2024 at 06:49:56PM +0530, Manali Shukla wrote: > > >>> + /* Check the extension for binary stats */ > > >>> + TEST_REQUIRE(this_cpu_has(X86_FEATURE_IDLE_HLT)); > > >> > > >> IIUC, this test assumes that the IDLE_HLT feature is enabled for guests if it > > >> is supported by the CPU. But this isn't true in some cases: > > >> > > >I understand you are intending to create a capability for IDLE HLT intercept > > >feature, but in my opinion, the IDLE Halt intercept feature doesn't require > > >user space to do anything for the feature itself. > > > > Yes, I agree. Actually, I was thinking about: > > > > 1. make the feature bit visible from /proc/cpuinfo by removing the leading "" > > from the comment following the bit definition in patch 1 > > > > 2. parse /proc/cpuinfo to determine if this IDLE_HLT feature is supported by the > > kernel > > Neither of these is sufficient/correct. E.g. they'll get false positives if run > on a kernel that recognizes IDLE_HLT, but that doesn't have KVM support for > enabling the feature. > > The canonical way to check for features in KVM selftests is kvm_cpu_has(), which > looks at KVM_GET_SUPPORTED_CPUID (by default, selftests VMs enable all features, > i.e. reflect the result of KVM_GET_SUPPORTED_CPUID into KVM_SET_CPUID2). Never mind, brain fart. That only works for features KVM is exposing to the guest, this is purely a KVM/host feature. That said, doesn't this test also require that AVIC be enabled? Oh, or does this happen to work because KVM uses V_INTR to detect interrupt windows?
