On Wed, Oct 27, 2021, Paolo Bonzini wrote: > On 27/10/21 17:06, Sean Christopherson wrote: > > > Does this still need to check the "running" flag? That should be a strict > > > superset of vcpu->mode == IN_GUEST_MODE. > > > > No. Signalling the doorbell when "running" is set but the vCPU is not in the > > guest is just an expensive nop. So even if KVM were to rework its handling of > > "running" to set the flag immediately before VMRUN and clear it immediately after, > > keying off IN_GUEST_MODE and not "running" would not be wrong, just sub-optimal. > > > > I doubt KVM will ever make the "running" flag super precise, because keeping the > > flag set when the vCPU is loaded avoids VM-Exits on other vCPUs due to undelivered > > IPIs. > > Right, so should we drop the "if (running)" check in this patch, at the same > time as it's adding the IN_GUEST_MODE check? LOL, I think we have a Three^WTwo Stooges routine going on. This patch does remove avic_vcpu_is_running() and replaces it with the vcpu->mode check. Or am I completely misunderstanding what your referring to? - if (avic_vcpu_is_running(vcpu)) { + /* + * Signal the doorbell to tell hardware to inject the IRQ if the vCPU + * is in the guest. If the vCPU is not in the guest, hardware will + * automatically process AVIC interrupts at VMRUN. + */ + if (vcpu->mode == IN_GUEST_MODE) { int cpu = READ_ONCE(vcpu->cpu); _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm