Sean Christopherson <seanjc@xxxxxxxxxx> writes: > This is what I ended up with as a way to dig ourselves out of the eVMCS > conundrum. Not well tested, though KUT and selftests pass. The enforcement > added by "KVM: nVMX: Enforce unsupported eVMCS in VMX MSRs for host accesses" > is not tested at all (and lacks a changelog). Trying to enable KVM_CAP_HYPERV_ENLIGHTENED_VMCS2 in its new shape in QEMU so I can test it and I immediately stumble upon ~/qemu/build/qemu-system-x86_64 -machine q35,accel=kvm,kernel-irqchip=split -cpu host,hv-evmcs-2022,hv-evmcs,hv-vpindex,hv-vapic qemu-system-x86_64: error: failed to set MSR 0x48d to 0xff00000016 qemu-system-x86_64: ../target/i386/kvm/kvm.c:3107: kvm_buf_set_msrs: Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed. Turns out, at least with "-cpu host" QEMU reads VMX feature MSRs first and enables eVMCS after. This is fixable, I believe but it makes me think that maybe eVMCS enablement (or even the whole Hyper-V emulation thing) should be per-VM as it makes really little sense to have Hyper-V features enabled on *some* vCPUs only. As we're going to add a new CAP anyway, maybe it's a good time to make a switch? -- Vitaly
