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:
make the feature bit visible from /proc/cpuinfo by removing the leading "" from the comment following the bit definition in patch 1
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?