From: Oliver Upton <oliver.upton@linux.dev>
To: Sean Christopherson <seanjc@google.com>
Cc: Marc Zyngier <maz@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Steve Rutherford <srutherford@google.com>
Subject: Re: [PATCH 2/2] KVM: Protect vCPU's "last run PID" with rwlock, not RCU
Date: Fri, 9 Aug 2024 11:05:49 -0700 [thread overview]
Message-ID: <ZrZafa66bRxoVc0Z@linux.dev> (raw)
In-Reply-To: <ZrK4x4LLz1wlwGQN@google.com>
On Tue, Aug 06, 2024 at 04:59:03PM -0700, Sean Christopherson wrote:
> > Can you nest this lock inside of the vcpu->mutex acquisition in
> > kvm_vm_ioctl_create_vcpu() so lockdep gets the picture?
>
> I don't think that's necessary. Commit 42a90008f890 ("KVM: Ensure lockdep knows
> about kvm->lock vs. vcpu->mutex ordering rule") added the lock+unlock in
> kvm_vm_ioctl_create_vcpu() purely because actually taking vcpu->mutex inside
> kvm->lock is rare, i.e. lockdep would be unable to detect issues except for very
> specific VM types hitting very specific flows.
I don't think the perceived rarity matters at all w/ this. Beyond the
lockdep benefits, it is a self-documenting way to describe lock ordering.
Dunno about you, but I haven't kept up with locking.rst at all :)
Having said that, an inversion would still be *very* obvious, as it
would be trying to grab a mutex while holding a spinlock...
--
Thanks,
Oliver
next prev parent reply other threads:[~2024-08-09 18:05 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-02 20:01 [PATCH 0/2] KVM: Protect vCPU's PID with a rwlock Sean Christopherson
2024-08-02 20:01 ` [PATCH 1/2] KVM: Return '0' directly when there's no task to yield to Sean Christopherson
2024-08-02 20:01 ` [PATCH 2/2] KVM: Protect vCPU's "last run PID" with rwlock, not RCU Sean Christopherson
2024-08-02 20:28 ` Steve Rutherford
2024-08-02 20:51 ` Sean Christopherson
2024-08-02 21:27 ` Steve Rutherford
2024-08-06 22:58 ` Oliver Upton
2024-08-06 23:59 ` Sean Christopherson
2024-08-09 18:05 ` Oliver Upton [this message]
2024-08-13 2:05 ` Sean Christopherson
2024-08-06 22:59 ` [PATCH 0/2] KVM: Protect vCPU's PID with a rwlock Oliver Upton
2024-10-31 19:51 ` Sean Christopherson
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