On Fri, Mar 31, 2017 at 06:06:57PM +0200, Andrew Jones wrote:
> From: Levente Kurusa <lkur...@redhat.com>
>
> When two vcpus issue PSCI_CPU_ON on the same core at the same time,
> then it's possible for them to both enter the target vcpu's setup
> at the same time. This results in unexpected behaviors at best,
> and the potential for some nasty bugs at worst.
>
> Signed-off-by: Levente Kurusa <lkur...@redhat.com>
> Signed-off-by: Andrew Jones <drjo...@redhat.com>
> ---
> arch/arm/kvm/psci.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
> index f732484abc7a..0204daa899b1 100644
> --- a/arch/arm/kvm/psci.c
> +++ b/arch/arm/kvm/psci.c
> @@ -88,7 +88,8 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu
> *source_vcpu)
> */
> if (!vcpu)
> return PSCI_RET_INVALID_PARAMS;
> - if (!test_bit(KVM_REQ_POWER_OFF, &vcpu->requests)) {
> +
> + if (!test_and_clear_bit(KVM_REQ_POWER_OFF, &vcpu->requests)) {
> if (kvm_psci_version(source_vcpu) != KVM_ARM_PSCI_0_1)
> return PSCI_RET_ALREADY_ON;
> else
> @@ -116,7 +117,6 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu
> *source_vcpu)
> * the general puspose registers are undefined upon CPU_ON.
> */
> vcpu_set_reg(vcpu, 0, context_id);
> - clear_bit(KVM_REQ_POWER_OFF, &vcpu->requests);
>
> wq = kvm_arch_vcpu_wq(vcpu);
> swake_up(wq);
> --
> 2.9.3
>
Depending on what you end up doing with the requests, if you keep the
bool flag you could just use the kvm->lock mutex instead.
Have you considered if there are any potential races between
kvm_psci_system_off() being called on one VCPU while two other VPCUs are
turning on the same CPU that is being turend off as part of system-wide
power down as well?
I'm wondering if this means we should take the kvm->lock at a higher
level when handling PSCI events...
Thanks,
-Christoffer
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