linux-kernel - Re: [RFC PATCH 0/5] KVM: guest_memfd: support for uffd missing

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Message-ID: <Z9R2JapHdhR2Xhp_@x1.local>
Date: Fri, 14 Mar 2025 14:32:05 -0400
From: Peter Xu <peterx@...hat.com>
To: Nikita Kalyazin <kalyazin@...zon.com>
Cc: James Houghton <jthoughton@...gle.com>, akpm@...ux-foundation.org,
	pbonzini@...hat.com, shuah@...nel.org, kvm@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, lorenzo.stoakes@...cle.com, david@...hat.com,
	ryan.roberts@....com, quic_eberman@...cinc.com, graf@...zon.de,
	jgowans@...zon.com, roypat@...zon.co.uk, derekmn@...zon.com,
	nsaenz@...zon.es, xmarcalx@...zon.com
Subject: Re: [RFC PATCH 0/5] KVM: guest_memfd: support for uffd missing

On Fri, Mar 14, 2025 at 05:12:35PM +0000, Nikita Kalyazin wrote:
> Yes, I was thinking about MADV_POPULATE_WRITE as well, but AFAIK it isn't
> available in guest_memfd, at least with direct map removed due to [1] being
> updated in [2]:

I see, so GUP is no-go.  IIUC the userapp can also prefault by writing
zeros in a loop after mmap().

Thanks,

-- 
Peter Xu