[lkml]   [2021]   [Oct]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v2 35/43] KVM: SVM: Signal AVIC doorbell iff vCPU is in guest mode
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?


 \ /
  Last update: 2021-10-27 17:36    [W:0.063 / U:3.108 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site