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KVM: arm64: Reset the PMU in preemptible context 

We've become very cautious to now always reset the vcpu when nothing
is loaded on the physical CPU. To do so, we now disable preemption
and do a kvm_arch_vcpu_put() to make sure we have all the state
in memory (and that it won't be loaded behind out back).

This now causes issues with resetting the PMU, which calls into perf.
Perf itself uses mutexes, which clashes with the lack of preemption.
It is worth realizing that the PMU is fully emulated, and that
no PMU state is ever loaded on the physical CPU. This means we can
perfectly reset the PMU outside of the non-preemptible section.

Fixes: e761a927bc ("KVM: arm/arm64: Reset the VCPU without preemption and vcpu state loaded")
Reported-by: Julien Grall <julien.grall@arm.com>
Tested-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
This commit is contained in:
Marc Zyngier 2019-03-04 17:37:44 +00:00
parent 9e98c678c2
commit ebff0b0e3d
1 changed files with 3 additions and 3 deletions
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6
arch/arm64/kvm/reset.c
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@ -123,6 +123,9 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
int ret = -EINVAL;
bool loaded;
/* Reset PMU outside of the non-preemptible section */
kvm_pmu_vcpu_reset(vcpu);
preempt_disable();
loaded = (vcpu->cpu != -1);
if (loaded)
@ -170,9 +173,6 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
vcpu->arch.reset_state.reset = false;
}
/* Reset PMU */
kvm_pmu_vcpu_reset(vcpu);
/* Default workaround setup is enabled (if supported) */
if (kvm_arm_have_ssbd() == KVM_SSBD_KERNEL)
vcpu->arch.workaround_flags |= VCPU_WORKAROUND_2_FLAG;