From: "Thomas Hellström (VMware)" <thomas_os@shipmail.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
dri-devel@lists.freedesktop.org, pv-drivers@vmware.com,
linux-graphics-maintainer@vmware.com,
"Thomas Hellstrom" <thellstrom@vmware.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
"Ralph Campbell" <rcampbell@nvidia.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Christian König" <christian.koenig@amd.com>
Subject: Re: [PATCH v2 2/2] drm/ttm: Fix vm page protection handling
Date: Wed, 4 Dec 2019 15:16:09 +0100 [thread overview]
Message-ID: <b29b166c-e9fe-f829-f533-b39f98b334a9@shipmail.org> (raw)
In-Reply-To: <20191204135219.GH25242@dhcp22.suse.cz>
On 12/4/19 2:52 PM, Michal Hocko wrote:
> On Tue 03-12-19 11:48:53, Thomas Hellström (VMware) wrote:
>> From: Thomas Hellstrom <thellstrom@vmware.com>
>>
>> TTM graphics buffer objects may, transparently to user-space, move
>> between IO and system memory. When that happens, all PTEs pointing to the
>> old location are zapped before the move and then faulted in again if
>> needed. When that happens, the page protection caching mode- and
>> encryption bits may change and be different from those of
>> struct vm_area_struct::vm_page_prot.
>>
>> 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.
> So essentially this should have any new side effect on functionality it
> is just making a hacky/ugly code less so?
Functionality is unchanged. The use of a on-stack vma copy was severely
frowned upon in an earlier thread, which also points to another similar
example using vmf_insert_pfn_prot().
https://lore.kernel.org/lkml/20190905103541.4161-2-thomas_os@shipmail.org/
> In other words what are the
> consequences of having page protection inconsistent from vma's?
During the years, it looks like the caching- and encryption flags of
vma::vm_page_prot have been largely removed from usage. From what I can
tell, there are no more places left that can affect TTM. We discussed
__split_huge_pmd_locked() towards the end of that thread, but that
doesn't affect TTM even with huge page-table entries.
/Thomas
next prev parent reply other threads:[~2019-12-04 14:16 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-03 10:48 [PATCH v2 0/2] mm, drm/ttm: Fix pte insertion with customized protection Thomas Hellström (VMware)
2019-12-03 10:48 ` [PATCH v2 1/2] mm: Add and export vmf_insert_mixed_prot() Thomas Hellström (VMware)
2019-12-04 13:48 ` Michal Hocko
2019-12-03 10:48 ` [PATCH v2 2/2] drm/ttm: Fix vm page protection handling Thomas Hellström (VMware)
2019-12-04 13:52 ` Michal Hocko
2019-12-04 14:16 ` Thomas Hellström (VMware) [this message]
2019-12-04 14:35 ` Michal Hocko
2019-12-04 14:36 ` Thomas Hellström (VMware)
2019-12-04 14:42 ` Michal Hocko
2019-12-04 15:19 ` Thomas Hellström (VMware)
2019-12-04 15:26 ` Michal Hocko
2019-12-04 15:29 ` Thomas Hellström (VMware)
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