On Mon, Apr 1, 2019 at 12:56 PM Liran Alon <liran.alon@xxxxxxxxxx> wrote:
>
>
>
> > On 1 Apr 2019, at 22:46, Jim Mattson <jmattson@xxxxxxxxxx> wrote:
> >
> > On Mon, Apr 1, 2019 at 7:51 AM Liran Alon <liran.alon@xxxxxxxxxx> wrote:
> >>
> >> Ping.
> >>
> >>> On 25 Mar 2019, at 21:09, Liran Alon <liran.alon@xxxxxxxxxx> wrote:
> >>>
> >>> Issue was discovered when running kvm-unit-tests on KVM running as L1 on
> >>> top of Hyper-V.
> >>>
> >>> When vmx_instruction_intercept unit-test attempts to run RDPMC to test
> >>> RDPMC-exiting, it is intercepted by L1 KVM which it's EXIT_REASON_RDPMC
> >>> handler raise #GP because vCPU exposed by Hyper-V doesn't support PMU.
> >>> Instead of unit-test expectation to be reflected with EXIT_REASON_RDPMC.
> >>>
> >>> The reason vmx_instruction_intercept unit-test attempts to run RDPMC
> >>> even though Hyper-V doesn't support PMU is because L1 expose to L2
> >>> support for RDPMC-exiting. Which is reasonable to assume that is
> >>> supported only in case CPU supports PMU to being with.
> >>>
> >>> Above issue can easily be simulated by modifying
> >>> vmx_instruction_intercept config in x86/unittests.cfg to run QEMU with
> >>> "-cpu host,+vmx,-pmu" and run unit-test.
> >>>
> >>> To handle issue, change KVM to expose RDPMC-exiting only when guest
> >>> supports PMU.
> >>>
> >>> Reported-by: Saar Amar <saaramar@xxxxxxxxxxxxx>
> >>> Reviewed-by: Mihai Carabas <mihai.carabas@xxxxxxxxxx>
> >>> Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx>
> >>> ---
> >>> arch/x86/kvm/vmx/vmx.c | 25 +++++++++++++++++++++++++
> >>> 1 file changed, 25 insertions(+)
> >>>
> >>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> >>> index f6915f10e584..2634ee8c9dc8 100644
> >>> --- a/arch/x86/kvm/vmx/vmx.c
> >>> +++ b/arch/x86/kvm/vmx/vmx.c
> >>> @@ -6978,6 +6978,30 @@ static void nested_vmx_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
> >>> }
> >>> }
> >>>
> >>> +static bool guest_cpuid_has_pmu(struct kvm_vcpu *vcpu)
> >>> +{
> >>> + struct kvm_cpuid_entry2 *entry;
> >>> + union cpuid10_eax eax;
> >>> +
> >>> + entry = kvm_find_cpuid_entry(vcpu, 0xa, 0);
> >>> + if (!entry)
> >>> + return false;
> >>> +
> >>> + eax.full = entry->eax;
> >>> + return (eax.split.version_id > 0);
> >>> +}
> >>> +
> >>> +static void nested_vmx_procbased_ctls_update(struct kvm_vcpu *vcpu)
> >>> +{
> >>> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> >>> + bool pmu_enabled = guest_cpuid_has_pmu(vcpu);
> >>> +
> >>> + if (pmu_enabled)
> >>> + vmx->nested.msrs.procbased_ctls_high |= CPU_BASED_RDPMC_EXITING;
> >
> > Doesn't this require that L0 supports RDPMC exiting, so that the bit
> > can be passed from vmcs12 to vmcs02?
>
> Looking at setup_vmcs_config(), CPU_BASED_RDPMC_EXITING is defined as part of minimum set of features
> that is required for KVM to run. So I can safely assume here that vmcs02 have RDPMC-exiting.
>
> Am I missing something?
> -Liran
No. That answers my question.
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
