linux-kernel - Re: [PATCH 2/2] drm/ttm: Fix vm page protection handling

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Message-ID: <5a8b8351-0960-305b-6606-96b673d7b729@shipmail.org>
Date:   Tue, 3 Dec 2019 11:19:21 +0100
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     Christian König <christian.koenig@....com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        pv-drivers@...are.com, linux-graphics-maintainer@...are.com,
        Thomas Hellstrom <thellstrom@...are.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>
Subject: Re: [PATCH 2/2] drm/ttm: Fix vm page protection handling

On 12/3/19 10:58 AM, Christian König wrote:
> Am 03.12.19 um 10:55 schrieb Kirill A. Shutemov:
>> On Tue, Dec 03, 2019 at 08:54:46AM +0100, Thomas Hellström (VMware) 
>> wrote:
>>> From: Thomas Hellstrom <thellstrom@...are.com>
>>>
>>> We were using an ugly hack to set the page protection correctly.
>>> Fix that and instead use vmf_insert_mixed_prot() and / or
>>> vmf_insert_pfn_prot().
>>> Also get the default page protection from
>>> struct vm_area_struct::vm_page_prot rather than using 
>>> vm_get_page_prot().
>>> This way we catch modifications done by the vm system for drivers that
>>> want write-notification.
>> Hm. Why doesn't your VMA have the right prot flags in the first 
>> place? Why
>> do you need to override them? More context, please.
>
> TTM allows for graphics buffer to move between system and IO memory. 
> So the prot flags can change on the fly for a VMA.
>
I'll add that and some additional info to the commit message. And fix 
that CC'd dri-devel address.

Thanks,
Thomas





> Regards,
> Christian.