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

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Message-ID: <20240802200136.329973-1-seanjc@google.com>
Date: Fri,  2 Aug 2024 13:01:34 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Sean Christopherson <seanjc@...gle.com>, Steve Rutherford <srutherford@...gle.com>
Subject: [PATCH 0/2] KVM: Protect vCPU's PID with a rwlock

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.

Extra eyeballs would be much appreciated.

Sean Christopherson (2):
  KVM: Return '0' directly when there's no task to yield to
  KVM: Protect vCPU's "last run PID" with rwlock, not RCU

 arch/arm64/include/asm/kvm_host.h |  2 +-
 include/linux/kvm_host.h          |  3 ++-
 virt/kvm/kvm_main.c               | 36 +++++++++++++++++--------------
 3 files changed, 23 insertions(+), 18 deletions(-)

base-commit: 332d2c1d713e232e163386c35a3ba0c1b90df83f
-- 
2.46.0.rc2.264.g509ed76dc8-goog