linux-kernel - Re: [PATCH RFC 0/5] mm/gup: Introduce exclusive GUP pinning

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Message-ID: <CAGtprH8VT6B6efy0dC=6cQEf6mpz3dfh2q4gGp2S-m+wNJn5ew@mail.gmail.com>
Date: Tue, 25 Jun 2024 20:19:12 -0700
From: Vishal Annapurve <vannapurve@...gle.com>
To: David Rientjes <rientjes@...gle.com>
Cc: Sean Christopherson <seanjc@...gle.com>, Elliot Berman <quic_eberman@...cinc.com>, 
	Fuad Tabba <tabba@...gle.com>, David Hildenbrand <david@...hat.com>, Jason Gunthorpe <jgg@...dia.com>, 
	John Hubbard <jhubbard@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Shuah Khan <shuah@...nel.org>, Matthew Wilcox <willy@...radead.org>, maz@...nel.org, 
	kvm@...r.kernel.org, linux-arm-msm@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	pbonzini@...hat.com
Subject: Re: [PATCH RFC 0/5] mm/gup: Introduce exclusive GUP pinning

On Mon, Jun 24, 2024 at 2:50 PM David Rientjes <rientjes@...gle.com> wrote:
>
> On Mon, 24 Jun 2024, Sean Christopherson wrote:
>
> > On Fri, Jun 21, 2024, Elliot Berman wrote:
> > > On Fri, Jun 21, 2024 at 11:16:31AM +0100, Fuad Tabba wrote:
> > > > On Fri, Jun 21, 2024 at 10:10 AM David Hildenbrand <david@...hat.com> wrote:
> > > > > On 21.06.24 10:54, Fuad Tabba wrote:
> > > > > > On Fri, Jun 21, 2024 at 9:44 AM David Hildenbrand <david@...hat.com> wrote:
> > > > > >>
> > > > > >>>> Again from that thread, one of most important aspects guest_memfd is that VMAs
> > > > > >>>> are not required.  Stating the obvious, lack of VMAs makes it really hard to drive
> > > > > >>>> swap, reclaim, migration, etc. from code that fundamentally operates on VMAs.
> > > > > >>>>
> > > > > >>>>    : More broadly, no VMAs are required.  The lack of stage-1 page tables are nice to
> > > > > >>>>    : have; the lack of VMAs means that guest_memfd isn't playing second fiddle, e.g.
> > > > > >>>>    : it's not subject to VMA protections, isn't restricted to host mapping size, etc.
> > > > > >>>>
> > > > > >>>> [1] https://lore.kernel.org/all/Zfmpby6i3PfBEcCV@google.com
> > > > > >>>> [2] https://lore.kernel.org/all/Zg3xF7dTtx6hbmZj@google.com
> > > > > >>>
> > > > > >>> I wonder if it might be more productive to also discuss this in one of
> > > > > >>> the PUCKs, ahead of LPC, in addition to trying to go over this in LPC.
> > > > > >>
> > > > > >> I don't know in  which context you usually discuss that, but I could
> > > > > >> propose that as a topic in the bi-weekly MM meeting.
> > > > > >>
> > > > > >> This would, of course, be focused on the bigger MM picture: how to mmap,
> > > > > >> how how to support huge pages, interaction with page pinning, ... So
> > > > > >> obviously more MM focused once we are in agreement that we want to
> > > > > >> support shared memory in guest_memfd and how to make that work with core-mm.
> > > > > >>
> > > > > >> Discussing if we want shared memory in guest_memfd might be betetr
> > > > > >> suited for a different, more CC/KVM specific meeting (likely the "PUCKs"
> > > > > >> mentioned here?).
> > > > > >
> > > > > > Sorry, I should have given more context on what a PUCK* is :) It's a
> > > > > > periodic (almost weekly) upstream call for KVM.
> > > > > >
> > > > > > [*] https://lore.kernel.org/all/20230512231026.799267-1-seanjc@google.com/
> > > > > >
> > > > > > But yes, having a discussion in one of the mm meetings ahead of LPC
> > > > > > would also be great. When do these meetings usually take place, to try
> > > > > > to coordinate across timezones.
> >
> > Let's do the MM meeting.  As evidenced by the responses, it'll be easier to get
> > KVM folks to join the MM meeting as opposed to other way around.
> >
> > > > > It's Wednesday, 9:00 - 10:00am PDT (GMT-7) every second week.
> > > > >
> > > > > If we're in agreement, we could (assuming there are no other planned
> > > > > topics) either use the slot next week (June 26) or the following one
> > > > > (July 10).
> > > > >
> > > > > Selfish as I am, I would prefer July 10, because I'll be on vacation
> > > > > next week and there would be little time to prepare.
> > > > >
> > > > > @David R., heads up that this might become a topic ("shared and private
> > > > > memory in guest_memfd: mmap, pinning and huge pages"), if people here
> > > > > agree that this is a direction worth heading.
> > > >
> > > > Thanks for the invite! Tentatively July 10th works for me, but I'd
> > > > like to talk to the others who might be interested (pKVM, Gunyah, and
> > > > others) to see if that works for them. I'll get back to you shortly.
> > > >
> > >
> > > I'd like to join too, July 10th at that time works for me.
> >
> > July 10th works for me too.
> >
>
> Thanks all, and David H for the topic suggestion.  Let's tentatively
> pencil this in for the Wednesday, July 10th instance at 9am PDT and I'll
> follow-up offlist with those will be needed to lead the discussion to make
> sure we're on track.

I would like to join the call too.

Regards,
Vishal