linux-kernel - Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages

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Message-ID: <a0d0ffd7-3c34-5002-f4fe-cb9d4ba0279e@amd.com>
Date:   Thu, 25 Mar 2021 13:09:14 +0100
From:   Christian König <christian.koenig@....com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>
Cc:     David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages

Am 25.03.21 um 13:01 schrieb Jason Gunthorpe:
> On Thu, Mar 25, 2021 at 12:53:15PM +0100, Thomas Hellström (Intel) wrote:
>
>> Nope. The point here was that in this case, to make sure mmap uses the
>> correct VA to give us a reasonable chance of alignement, the driver might
>> need to be aware of and do trickery with the huge page-table-entry sizes
>> anyway, although I think in most cases a standard helper for this can be
>> supplied.
> Of course the driver needs some way to influence the VA mmap uses,
> gernally it should align to the natural page size of the device

Well a mmap() needs to be aligned to the page size of the CPU, but not 
necessarily to the one of the device.

So I'm pretty sure the device driver should not be involved in any way 
the choosing of the VA for the CPU mapping.

Christian.

>
> Jason