linux-kernel - Re: [PATCH v3 00/15] KVM: Introduce KVM Userfault

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Message-ID: <aFNKuGVWGn0dzKuV@linux.dev>
Date: Wed, 18 Jun 2025 16:24:40 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: James Houghton <jthoughton@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>,
	Yan Zhao <yan.y.zhao@...el.com>,
	Nikita Kalyazin <kalyazin@...zon.com>,
	Anish Moorthy <amoorthy@...gle.com>,
	Peter Gonda <pgonda@...gle.com>, Peter Xu <peterx@...hat.com>,
	David Matlack <dmatlack@...gle.com>, wei.w.wang@...el.com,
	kvm@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev
Subject: Re: [PATCH v3 00/15] KVM: Introduce KVM Userfault

On Wed, Jun 18, 2025 at 04:24:09AM +0000, James Houghton wrote:
> Hi Sean, Paolo, Oliver, + others,
> 
> Here is a v3 of KVM Userfault. Thanks for all the feedback on the v2,
> Sean. I realize it has been 6 months since the v2; I hope that isn't an
> issue.

Not one bit. The only thing I look for in patch frequency is the urgency
with which the author wants to get something in.

> I am working on the QEMU side of the changes as I get time. Let me know
> if it's important for me to send those patches out for this series to be
> merged.

It'd be good to know we have line of sight on a functional
implementation here, i.e. uffd-based handling of non-vCPU accesses. I'm
not expecting surprises here, but patches always speak louder than
words.

Don't want to block the kernel pieces if that's a time sink though. And
FWIW, besides the nitpicking I'm quite happy with the way this is
shaping up.

> Be aware that this series will have non-trivial conflicts with Fuad's
> user mapping support for guest_memfd series[1]. For example, for the
> arm64 change he is making, the newly introduced gmem_abort() would need
> to be enlightened to handle KVM Userfault exits.

Appreciate the heads up!

Thanks,
Oliver