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Date: Tue, 6 Feb 2024 20:22:07 -0800
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Subject: Re: [PATCH v12 18/20] KVM: pfncache: check the need for invalidation
 under read lock first
From: Sean Christopherson <seanjc@google.com>
To: Paul Durrant <paul@xen.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Jonathan Corbet <corbet@lwn.net>, 
	Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, 
	Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, 
	"H. Peter Anvin" <hpa@zytor.com>, David Woodhouse <dwmw2@infradead.org>, Shuah Khan <shuah@kernel.org>, 
	kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-kselftest@vger.kernel.org
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On Mon, Jan 15, 2024, Paul Durrant wrote:
> From: Paul Durrant <pdurrant@amazon.com>
> 
> Taking a write lock on a pfncache will be disruptive if the cache is

*Unnecessarily* taking a write lock.  Please save readers a bit of brain power
and explain that this is beneificial when there are _unrelated_ invalidation.

> heavily used (which only requires a read lock). Hence, in the MMU notifier
> callback, take read locks on caches to check for a match; only taking a
> write lock to actually perform an invalidation (after a another check).

This doesn't have any dependency on this series, does it?  I.e. this should be
posted separately, and preferably with some performance data.  Not having data
isn't a sticking point, but it would be nice to verify that this isn't a
pointless optimization.