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From: "Williams, Dan J" <dan.j.williams@intel.com>
To: "dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"thomas_os@shipmail.org" <thomas_os@shipmail.org>
Cc: "daniel@ffwll.ch" <daniel@ffwll.ch>,
	"christian.koenig@amd.com" <christian.koenig@amd.com>,
	"jgg@nvidia.com" <jgg@nvidia.com>,
	"airlied@linux.ie" <airlied@linux.ie>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages
Date: Tue, 23 Mar 2021 19:52:13 +0000	[thread overview]
Message-ID: <ec99146c7abc35d16b245816aba3e9d14862e624.camel@intel.com> (raw)
In-Reply-To: <20210321184529.59006-2-thomas_os@shipmail.org>

On Sun, 2021-03-21 at 19:45 +0100, Thomas Hellström (Intel) wrote:
> TTM sets up huge page-table-entries both to system- and device
> memory,
> and we don't want gup to assume there are always valid backing struct
> pages for these. For PTEs this is handled by setting the pte_special
> bit,
> but for the huge PUDs and PMDs, we have neither pmd_special nor
> pud_special. Normally, huge TTM entries are identified by looking at
> vma_is_special_huge(), but fast gup can't do that, so as an
> alternative
> define _devmap entries for which there are no backing dev_pagemap as
> special, update documentation and make huge TTM entries _devmap,
> after
> verifying that there is no backing dev_pagemap.

Please do not abuse p{m,u}d_devmap like this. I'm in the process of
removing get_devpagemap() from the gup-fast path [1]. Instead there
should be space for p{m,u}d_special in the page table entries (at least
for x86-64). So the fix is to remove that old assumption that huge
pages can never be special.

[1]: 
http://lore.kernel.org/r/161604050866.1463742.7759521510383551055.stgit@dwillia2-desk3.amr.corp.intel.com


  parent reply	other threads:[~2021-03-23 19:52 UTC|newest]

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-21 18:45 [RFC PATCH 0/2] mm,drm/ttm: Always block GUP to TTM pages Thomas Hellström (Intel)
2021-03-21 18:45 ` [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages Thomas Hellström (Intel)
2021-03-23 11:34   ` Daniel Vetter
2021-03-23 16:34     ` Thomas Hellström (Intel)
2021-03-23 16:37       ` Jason Gunthorpe
2021-03-23 16:59         ` Christoph Hellwig
2021-03-23 17:06         ` Thomas Hellström (Intel)
2021-03-24  9:56           ` Daniel Vetter
2021-03-24 12:24             ` Jason Gunthorpe
2021-03-24 12:35               ` Thomas Hellström (Intel)
2021-03-24 12:41                 ` Jason Gunthorpe
2021-03-24 13:35                   ` Thomas Hellström (Intel)
2021-03-24 13:48                     ` Jason Gunthorpe
2021-03-24 15:50                       ` Thomas Hellström (Intel)
2021-03-24 16:38                         ` Jason Gunthorpe
2021-03-24 18:31                           ` Christian König
2021-03-24 20:07                             ` Thomas Hellström (Intel)
2021-03-24 23:14                               ` Jason Gunthorpe
2021-03-25  7:48                                 ` Thomas Hellström (Intel)
2021-03-25  8:27                                   ` Christian König
2021-03-25  9:51                                     ` Thomas Hellström (Intel)
2021-03-25 11:30                                       ` Jason Gunthorpe
2021-03-25 11:53                                         ` Thomas Hellström (Intel)
2021-03-25 12:01                                           ` Jason Gunthorpe
2021-03-25 12:09                                             ` Christian König
2021-03-25 12:36                                               ` Thomas Hellström (Intel)
2021-03-25 13:02                                                 ` Christian König
2021-03-25 13:31                                                   ` Thomas Hellström (Intel)
2021-03-25 12:42                                               ` Jason Gunthorpe
2021-03-25 13:05                                                 ` Christian König
2021-03-25 13:17                                                   ` Jason Gunthorpe
2021-03-25 13:26                                                     ` Christian König
2021-03-25 13:33                                                       ` Jason Gunthorpe
2021-03-25 13:54                                                         ` Christian König
2021-03-25 13:56                                                           ` Jason Gunthorpe
2021-03-25  7:49                                 ` Christian König
2021-03-25  9:41                                   ` Daniel Vetter
2021-03-23 13:52   ` Jason Gunthorpe
2021-03-23 15:05     ` Thomas Hellström (Intel)
2021-03-23 19:52   ` Williams, Dan J [this message]
2021-03-23 20:42     ` Thomas Hellström (Intel)
2021-03-24  9:58       ` Daniel Vetter
2021-03-24 10:05         ` Thomas Hellström (Intel)
     [not found]           ` <75423f64-adef-a2c4-8e7d-2cb814127b18@intel.com>
2021-03-24 20:22             ` Thomas Hellström (Intel)
2021-03-24 20:25               ` Dave Hansen
2021-03-25 17:51                 ` Thomas Hellström (Intel)
2021-03-25 17:55                   ` Jason Gunthorpe
2021-03-25 18:13                     ` Thomas Hellström (Intel)
2021-03-25 18:24                       ` Jason Gunthorpe
2021-03-25 18:42                         ` Thomas Hellström (Intel)
2021-03-26  9:08                         ` Thomas Hellström (Intel)
2021-03-26 11:46                           ` Jason Gunthorpe
2021-03-26 12:33                             ` Thomas Hellström (Intel)
2021-03-21 18:45 ` [RFC PATCH 2/2] mm,drm/ttm: Use VM_PFNMAP for TTM vmas Thomas Hellström (Intel)
2021-03-22  7:47   ` Christian König
2021-03-22  8:13     ` Thomas Hellström (Intel)
2021-03-23 11:57       ` Christian König
2021-03-23 11:47   ` Daniel Vetter
2021-03-23 14:04     ` Jason Gunthorpe
2021-03-23 15:51       ` Thomas Hellström (Intel)
2021-03-23 14:00   ` Jason Gunthorpe
2021-03-23 15:46     ` Thomas Hellström (Intel)
2021-03-23 16:06       ` Jason Gunthorpe

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