On Wed, 18 Aug 2021 09:50:44 +0100,
Oliver Upton <oupton@xxxxxxxxxx> wrote:
>
> KVM correctly serializes writes to a vCPU's reset state, however since
> we do not take the KVM lock on the read side it is entirely possible to
> read state from two different reset requests.
>
> Cure the race for now by taking the KVM lock when reading the
> reset_state structure.
>
> Fixes: 358b28f09f0a ("arm/arm64: KVM: Allow a VCPU to fully reset itself")
> Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
> ---
> arch/arm64/kvm/reset.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 18ffc6ad67b8..3507e64ff8ad 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -210,10 +210,16 @@ static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
> */
> int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> {
> + struct vcpu_reset_state reset_state;
> int ret;
> bool loaded;
> u32 pstate;
>
> + mutex_lock(&vcpu->kvm->lock);
> + memcpy(&reset_state, &vcpu->arch.reset_state, sizeof(reset_state));
nit: "reset_state = vcpu->arch.reset_state;" should do the trick.
> + vcpu->arch.reset_state.reset = false;
We should probably need to upgrade this to a WRITE_ONCE() to match the
PSCI side.
> + mutex_unlock(&vcpu->kvm->lock);
> +
> /* Reset PMU outside of the non-preemptible section */
> kvm_pmu_vcpu_reset(vcpu);
>
> @@ -276,8 +282,8 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> * Additional reset state handling that PSCI may have imposed on us.
> * Must be done after all the sys_reg reset.
> */
> - if (vcpu->arch.reset_state.reset) {
> - unsigned long target_pc = vcpu->arch.reset_state.pc;
> + if (reset_state.reset) {
> + unsigned long target_pc = reset_state.pc;
>
> /* Gracefully handle Thumb2 entry point */
> if (vcpu_mode_is_32bit(vcpu) && (target_pc & 1)) {
> @@ -286,13 +292,11 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> }
>
> /* Propagate caller endianness */
> - if (vcpu->arch.reset_state.be)
> + if (reset_state.be)
> kvm_vcpu_set_be(vcpu);
>
> *vcpu_pc(vcpu) = target_pc;
> - vcpu_set_reg(vcpu, 0, vcpu->arch.reset_state.r0);
> -
> - vcpu->arch.reset_state.reset = false;
> + vcpu_set_reg(vcpu, 0, reset_state.r0);
> }
>
> /* Reset timer */
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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