Re: [PATCH 0/2] KVM: Protect vCPU's PID with a rwlock

[Sean Christopherson]

On Fri, 02 Aug 2024 13:01:34 -0700, Sean Christopherson wrote:
> Protect vcpu->pid with a rwlock instead of RCU, so that running a vCPU
> with a different task doesn't require a full RCU synchronization, which
> can introduce a non-trivial amount of jitter, especially on large systems.
> 
> I've had this mini-series sitting around for ~2 years, pretty much as-is.
> I could have sworn past me thought there was a flaw in using a rwlock, and
> so I never posted it, but for the life of me I can't think of any issues.
> 
> [...]

Applied to kvm-x86 generic, with a comment explaining the vcpu->mutex is the
true protector of vcpu->pid.

Oliver, I didn't add the requested lockdep notification, I really want to make
that a separate discussion:

https://lore.kernel.org/all/20241009150455.1057573-7-seanjc@xxxxxxxxxx

[1/2] KVM: Return '0' directly when there's no task to yield to
      https://github.com/kvm-x86/linux/commit/6cf9ef23d942
[2/2] KVM: Protect vCPU's "last run PID" with rwlock, not RCU
      https://github.com/kvm-x86/linux/commit/3e7f43188ee2

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https://github.com/kvm-x86/linux/tree/next