linux-kernel - Re: [RFC PATCH 26/39] KVM: guest_memfd: Track faultability within a struct kvm_gmem

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Message-ID: <CAGtprH-xdXCMSwnE9umz1CHgT2A83AM+w-GJxPp4y99FKpgVtQ@mail.gmail.com>
Date: Thu, 17 Oct 2024 23:56:19 +0530
From: Vishal Annapurve <vannapurve@...gle.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: David Hildenbrand <david@...hat.com>, Peter Xu <peterx@...hat.com>, 
	Ackerley Tng <ackerleytng@...gle.com>, tabba@...gle.com, quic_eberman@...cinc.com, 
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	linux-mm@...ck.org, kvm@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH 26/39] KVM: guest_memfd: Track faultability within a
 struct kvm_gmem_private

On Thu, Oct 17, 2024 at 10:46 PM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> On Thu, Oct 17, 2024 at 07:11:46PM +0200, David Hildenbrand wrote:
> > On 17.10.24 18:47, Jason Gunthorpe wrote:
> > > On Thu, Oct 17, 2024 at 10:58:29AM -0400, Peter Xu wrote:
> > >
> > > > My question was more torwards whether gmemfd could still expose the
> > > > possibility to be used in VA forms to other modules that may not support
> > > > fd+offsets yet.
> > >
> > > I keep hearing they don't want to support page pinning on a guestmemfd
> > > mapping, so VA based paths could not work.
> >
> > For shared pages it absolutely must work. That's what I keep hearing :)
>
> Oh that's confusing. I assume non longterm pins desired on shared
> pages though??
>
> Jason

For hugepage support to work, longterm pins on guest private pages
need to be avoided [1], If this somehow was the cause of any confusion
here.

[1] https://lpc.events/event/18/contributions/1764/attachments/1409/3182/LPC%202024_%201G%20page%20support%20for%20guest_memfd.pdf
(slide 12)