On Tue, Feb 04, 2025 at 09:51:22AM -0800, Sean Christopherson wrote: > On Tue, Feb 04, 2025, Naveen N Rao wrote: > > On Mon, Feb 03, 2025 at 09:00:05PM -0500, Maxim Levitsky wrote: > > > On Mon, 2025-02-03 at 22:33 +0530, Naveen N Rao (AMD) wrote: > > > > apicv_update_lock is not required when querying the state of guest > > > > debug in all the vcpus. Remove usage of the same, and switch to > > > > kvm_set_or_clear_apicv_inhibit() helper to simplify the code. > > > > > > It might be worth to mention that the reason why the lock is not needed, > > > is because kvm_vcpu_ioctl from which this function is called takes 'vcpu->mutex' > > > and thus concurrent execution of this function is not really possible. > > > > Looking at this again, that looks to be a vcpu-specific lock, so I guess > > it is possible for multiple vcpus to run this concurrently? > > Correct. > > > In reality, this looks to be coming in from a vcpu ioctl from userspace, > > so this is probably not being invoked concurrently today. > > > > Regardless, I wonder if moving this to a per-vcpu inhibit might be a > > better way to address this. > > No, this is a slow path. My comment was more from the point of view of correctness, rather than performance (with the goal of removing use of apicv_update_lock) -- similar to the issue with IRQWIN needing to maintain per-vcpu state. My naive understanding of Maxim's mail was that we would introduce per-vcpu inhibit field to maintain per-vcpu inhibit state, but not actually inhibit AVIC on a per-vcpu basis :) Thanks, Naveen
