linux-kernel - Re: [PATCH v1 1/4] mm/hmm: HMM API for P2P DMA to device zone pages

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Message-ID: <20241017115304.GH4020792@ziepe.ca>
Date: Thu, 17 Oct 2024 08:53:04 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Alistair Popple <apopple@...dia.com>
Cc: Yonatan Maman <ymaman@...dia.com>, nouveau@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	linux-mm@...ck.org, herbst@...hat.com, lyude@...hat.com,
	dakr@...hat.com, airlied@...il.com, simona@...ll.ch,
	leon@...nel.org, jglisse@...hat.com, akpm@...ux-foundation.org,
	dri-devel@...ts.freedesktop.org, bskeggs@...dia.com,
	Gal Shalom <GalShalom@...dia.com>
Subject: Re: [PATCH v1 1/4] mm/hmm: HMM API for P2P DMA to device zone pages

On Thu, Oct 17, 2024 at 12:58:48PM +1100, Alistair Popple wrote:

> Actually I think the rule should be don't look at the page at
> all. hmm_range_fault() is about mirroring PTEs, no assumption should
> even be made about the existence or otherwise of a struct page.

We are not there yet..
 
> > We don't need to enforce, it we don't know what else the driver will
> > want to use that P2P page for after all. It might stick it in a VMA
> > for some unrelated reason.
> 
> And wouldn't that touch the refcount and therefore be wrong?

I mean the originating driver would do that

Jason