> 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
>
>>> + else
>>> + vmx->nested.msrs.procbased_ctls_high &= ~CPU_BASED_RDPMC_EXITING;
>>> +}
>>> +
>>> static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
>>> {
>>> struct vcpu_vmx *vmx = to_vmx(vcpu);
>>> @@ -7066,6 +7090,7 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
>>> if (nested_vmx_allowed(vcpu)) {
>>> nested_vmx_cr_fixed1_bits_update(vcpu);
>>> nested_vmx_entry_exit_ctls_update(vcpu);
>>> + nested_vmx_procbased_ctls_update(vcpu);
>>> }
>>>
>>> if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&
>>> --
>>> 2.20.1
>>>
>>
