linux-kernel - Re: [PATCH 0/9] Add support for SVM atomics in Nouveau

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Message-ID: <6616185.Wbe1NtApLk@nvdebian>
Date:   Thu, 18 Feb 2021 10:00:54 +1100
From:   Alistair Popple <apopple@...dia.com>
To:     <linux-mm@...ck.org>
CC:     Christoph Hellwig <hch@...radead.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Daniel Vetter <daniel@...ll.ch>,
        "Nouveau Dev" <nouveau@...ts.freedesktop.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        <kvm-ppc@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        Jerome Glisse <jglisse@...hat.com>
Subject: Re: [PATCH 0/9] Add support for SVM atomics in Nouveau

On Thursday, 11 February 2021 6:55:10 PM AEDT Christoph Hellwig wrote:
> On Wed, Feb 10, 2021 at 01:59:13PM -0400, Jason Gunthorpe wrote:
> > Really what you want to do here is leave the CPU page in the VMA and
> > the page tables where it started and deny CPU access to the page. Then
> > all the proper machinery will continue to work.
> > 
> > IMHO "migration" is the wrong idea if the data isn't actually moving.
> 
> Agreed.
 
I chose "migration" because device private pages seemed like a good way of 
reusing existing code to do what was required (a callback on CPU access).

However I have been reworking this to use mmu notifiers as the callback and it 
seems to simplify some things nicely so think I also agree. It removes the 
requirement for the pin as well which is nice, I'll post it as a v2 soon.

 - Alistair