[PATCH 3/8] KVM: arm64: Refuse illegal KVM_ARM_VCPU_PMU_V3 at reset time
Marc Zyngier
maz at kernel.org
Thu Nov 26 10:25:24 EST 2020
Hi Alex,
On 2020-11-26 14:59, Alexandru Elisei wrote:
> Hi Marc,
>
> On 11/13/20 6:25 PM, Marc Zyngier wrote:
>> We accept to configure a PMU when a vcpu is created, even if the
>> HW (or the host) doesn't support it. This results in failures
>> when attributes get set, which is a bit odd as we should have
>> failed the vcpu creation the first place.
>>
>> Move the check to the point where we check the vcpu feature set,
>> and fail early if we cannot support a PMU. This further simplifies
>> the attribute handling.
>>
>> Signed-off-by: Marc Zyngier <maz at kernel.org>
>> ---
>> arch/arm64/kvm/pmu-emul.c | 4 ++--
>> arch/arm64/kvm/reset.c | 4 ++++
>> 2 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
>> index e7e3b4629864..200f2a0d8d17 100644
>> --- a/arch/arm64/kvm/pmu-emul.c
>> +++ b/arch/arm64/kvm/pmu-emul.c
>> @@ -913,7 +913,7 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int
>> irq)
>>
>> int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct
>> kvm_device_attr *attr)
>> {
>> - if (!kvm_arm_support_pmu_v3() || !kvm_vcpu_has_pmu(vcpu))
>> + if (!kvm_vcpu_has_pmu(vcpu))
>> return -ENODEV;
>>
>> if (vcpu->arch.pmu.created)
>> @@ -1034,7 +1034,7 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu
>> *vcpu, struct kvm_device_attr *attr)
>> case KVM_ARM_VCPU_PMU_V3_IRQ:
>> case KVM_ARM_VCPU_PMU_V3_INIT:
>> case KVM_ARM_VCPU_PMU_V3_FILTER:
>> - if (kvm_arm_support_pmu_v3() && kvm_vcpu_has_pmu(vcpu))
>> + if (kvm_vcpu_has_pmu(vcpu))
>> return 0;
>> }
>>
>> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
>> index 74ce92a4988c..3e772ea4e066 100644
>> --- a/arch/arm64/kvm/reset.c
>> +++ b/arch/arm64/kvm/reset.c
>> @@ -285,6 +285,10 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
>> pstate = VCPU_RESET_PSTATE_EL1;
>> }
>>
>> + if (kvm_vcpu_has_pmu(vcpu) && !kvm_arm_support_pmu_v3()) {
>> + ret = -EINVAL;
>> + goto out;
>> + }
>
> This looks correct, but right at the beginning of the function, before
> this
> non-preemptible section, we do kvm_pmu_vcpu_reset(), which is wrong for
> several
> reasons:
>
> - we don't check if the feature flag is set
> - we don't check if the hardware supports a PMU
> - kvm_pmu_vcpu_reset() relies on __vcpu_sys_reg(vcpu, PMCR_EL0), which
> is set in
> kvm_reset_sys_regs() below when the VCPU is initialized.
I'm not sure it actually matters. Here's my rational:
- PMU support not compiled in: no problem!
- PMU support compiled in, but no HW PMU: we just reset some state to 0,
no harm done
- HW PMU, but no KVM PMU for this vcpu: same thing
- HW PMU, and KVM PMU: we do the right thing!
Am I missing anything?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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