Hi Marc,
On Tue, Apr 12, 2022 at 02:12:59PM +0100, Marc Zyngier wrote:
> For WFxT instructions used with very small delays, it is not
> unlikely that the deadling is already expired by the time we
typo: deadline
> reach the WFx handling code.
>
> Check for this condition as soon as possible, and return to the
> guest immediately if we can.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> arch/arm64/kvm/handle_exit.c | 25 ++++++++++++++++++++++---
> 1 file changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 4260f2cd1971..87d9a36de860 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -80,17 +80,34 @@ static int handle_no_fpsimd(struct kvm_vcpu *vcpu)
> *
> * @vcpu: the vcpu pointer
> *
> - * WFE: Yield the CPU and come back to this vcpu when the scheduler
> + * WFE[T]: Yield the CPU and come back to this vcpu when the scheduler
> * decides to.
> * WFI: Simply call kvm_vcpu_halt(), which will halt execution of
> * world-switches and schedule other host processes until there is an
> * incoming IRQ or FIQ to the VM.
> * WFIT: Same as WFI, with a timed wakeup implemented as a background timer
> + *
> + * WF{I,E}T can immediately return if the deadline has already expired.
> */
> static int kvm_handle_wfx(struct kvm_vcpu *vcpu)
> {
> u64 esr = kvm_vcpu_get_esr(vcpu);
>
> + if (esr & ESR_ELx_WFx_ISS_WFxT) {
> + if (esr & ESR_ELx_WFx_ISS_RV) {
> + u64 val, now;
> +
> + now = kvm_arm_timer_get_reg(vcpu, KVM_REG_ARM_TIMER_CNT);
> + val = vcpu_get_reg(vcpu, kvm_vcpu_sys_get_rt(vcpu));
> +
> + if (now >= val)
> + goto out;
If this returns early, the trace_kvm_wfx and wfx_exit_stats below will not be
called / updated. Is this intentional?
> + } else {
> + /* Treat WFxT as WFx if RN is invalid */
> + esr &= ~ESR_ELx_WFx_ISS_WFxT;
> + }
> + }
> +
> if (esr & ESR_ELx_WFx_ISS_WFE) {
> trace_kvm_wfx_arm64(*vcpu_pc(vcpu), true);
> vcpu->stat.wfe_exit_stat++;
> @@ -98,11 +115,13 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu)
> } else {
> trace_kvm_wfx_arm64(*vcpu_pc(vcpu), false);
> vcpu->stat.wfi_exit_stat++;
> - if ((esr & (ESR_ELx_WFx_ISS_RV | ESR_ELx_WFx_ISS_WFxT)) == (ESR_ELx_WFx_ISS_RV | ESR_ELx_WFx_ISS_WFxT))
> +
> + if (esr & ESR_ELx_WFx_ISS_WFxT)
> vcpu->arch.flags |= KVM_ARM64_WFIT;
> +
> kvm_vcpu_wfi(vcpu);
> }
> -
> +out:
> kvm_incr_pc(vcpu);
>
> return 1;
Thanks,
Joey
