linux-kernel - Re: [PATCH v4 0/2] KVM: guest_memfd: use write for population

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Message-ID: <ffe2f73a-6938-4079-b926-9d869f0642ca@redhat.com>
Date: Thu, 28 Aug 2025 22:07:35 +0200
From: David Hildenbrand <david@...hat.com>
To: "Kalyazin, Nikita" <kalyazin@...zon.co.uk>,
 "pbonzini@...hat.com" <pbonzini@...hat.com>,
 "shuah@...nel.org" <shuah@...nel.org>
Cc: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "michael.day@....com" <michael.day@....com>,
 "jthoughton@...gle.com" <jthoughton@...gle.com>,
 "Roy, Patrick" <roypat@...zon.co.uk>, "Thomson, Jack"
 <jackabt@...zon.co.uk>, "Manwaring, Derek" <derekmn@...zon.com>,
 "Cali, Marco" <xmarcalx@...zon.co.uk>
Subject: Re: [PATCH v4 0/2] KVM: guest_memfd: use write for population

On 28.08.25 17:30, Kalyazin, Nikita wrote:
> [ based on kvm/next ]
> 
> Implement guest_memfd allocation and population via the write syscall.
> This is useful in non-CoCo use cases where the host can access guest
> memory.  Even though the same can also be achieved via userspace mapping
> and memcpying from userspace, write provides a more performant option
> because it does not need to set page tables and it does not cause a page
> fault for every page like memcpy would.  Note that memcpy cannot be
> accelerated via MADV_POPULATE_WRITE as it is not supported by
> guest_memfd and relies on GUP.

I also added this patch to the pile of guestmemfd preview patches located at

https://git.kernel.org/pub/scm/linux/kernel/git/david/linux.git/log/?h=guestmemfd-preview

There was only one minor conflict regarding setting file->f_mode.

-- 
Cheers

David / dhildenb