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Mon, 12 Oct 2020 10:46:39 +0000 (GMT) Subject: Re: [PATCH v2 09/17] mm: Add unsafe_follow_pfn To: Jason Gunthorpe , Mauro Carvalho Chehab Cc: Daniel Vetter , DRI Development , LKML , kvm@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org, linux-s390@vger.kernel.org, Daniel Vetter , Kees Cook , Dan Williams , Andrew Morton , John Hubbard , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jan Kara , Linus Torvalds From: Marek Szyprowski Message-ID: Date: Mon, 12 Oct 2020 12:46:39 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.3.2 MIME-Version: 1.0 In-Reply-To: <20201009124850.GP5177@ziepe.ca> Content-Transfer-Encoding: 7bit Content-Language: en-US X-Brightmail-Tracker: H4sIAAAAAAAAA02Sa0hTYRjHec85OzuOjhyn4oNFxbpRoCbdXrCiNOVQFH0LirKpB4vcss1p 2oekRdpcYUaoc6TTIhXNWl5CzWxZ02ZmZillmaag0hxoGtrV4+nit99z/f+fl5chlRfpQOa4 NknQadUJKlpB1T6d6Qjy2Xg+er2rTomtVRU0zr3WibBt4D2Jb7XfJnH3lIfGBblGAufntaI5 GiHw3eFiOW7P0mDrtVPY/umNDL+qt9LYfKdGhj9U/JLhbJuRxHkvmgg8UPAa4cHLbvkOX74g /SXFP5guoviSxlGCt5dfpHn7RI6cb837RvH9WU6Cv3fjLH/JOE7znqbXNN9e1CLnJ+1L+ZrJ d9R+9qBia5yQcDxZ0IVsP6o4NpHtpBN/0Kcflo4Q6ahRZkIMA9xGyOkMMyEvRsmVIpgdjzIh xRx/QWAaKKGkwiSCjCmZyGL/cP1HWmq6haCizYOkwIPA0VkxP+HLbYG+J9OEyH7cASi6IW5S MCRnlMHg9StysUBzoWBym2jRBstth8ruQ2Ka4laB2d2LRPbnYuCF7TspMsv5QFv+0Px+Ly4I Zt1l83mSWwZ1busfDoC3Q4WEqAVcMwOjrW9JyfYuGB+zERL7wpizWi7xEnBdNVPSgBHBQEel XArMCF6dy0NSVxj0dczOOyW5tVBVHyK93U543KCW0Bt63T6SB2/Iqc0lpTQLmReU0o7VYHHe /qf6qLOLzEYqy4LLLAuusSy4xvJftghR5ShAMOg18YI+VCukBOvVGr1BGx8ce1JjR3Mf1PXT OXEfTXXFOBDHINUiNjHCGK2UqZP1qRoHAoZU+bHhz11HlGycOjVN0J2M1hkSBL0DLWYoVQC7 oXj0sJKLVycJJwQhUdD9rRKMV2A6upxURpRfiE5xzbasfFmf2e248752RY/WusY+EcKzQa2b yxo6DpcUbjhjWW77OtPbn6gtbTQwM9kz+5oViyKqlHt6qm8u3/Q55np3w7SqkoGowL4+7wB3 msF4IKs8rCXKHbkpvTh8d2FwV+xdT4H227Yll3qeP/PfmzEZWRlizo9QUfpj6tB1pE6v/g39 D1qlnAMAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprPKsWRmVeSWpSXmKPExsVy+t/xu7oCJi3xBgd/61vMWb+GzWL61AuM Fgsf3mW2WH5mHbPFla/v2SxmT29mspg54wQjkPWCyWLj00XsFme6cy3mTC202PT4GqvF5V1z 2Cx6Nmxltbi35j+rxYSFzcwWM87vY7J4OPsqo8WjvrfsDsIesxsusnjs/baAxWPxnpdMHptW dbJ5bPo0id3jxIzfLB73u48zeWxeUu/R2/yOzeP9vqtsHmcWHGH3+LxJzmPr59ssAbxRejZF +aUlqQoZ+cUltkrRhhZGeoaWFnpGJpZ6hsbmsVZGpkr6djYpqTmZZalF+nYJehmfJhxnK/jL VrF/xQumBsY9rF2MnBwSAiYST3c9YOti5OIQEljKKPFpwUI2iISMxMlpDVBFwhJ/rnVBFb1l lFiy/T1YkbCAucSdo9+YQGwRgXCJFde2sYAUMQu0skr0f3/FCtFxhUniw4YFLCBVbAKGEl1v QUZxcPAK2EmsvRINEmYRUJXoeXuDEcQWFUiS+H61C8zmFRCUODnzCVgrp4CuxK+3K5lBbGYB M4l5mx9C2fIS29/OgbLFJW49mc80gVFoFpL2WUhaZiFpmYWkZQEjyypGkdTS4tz03GJDveLE 3OLSvHS95PzcTYzAxLHt2M/NOxgvbQw+xCjAwajEw1vg3BwvxJpYVlyZe4hRgoNZSYTX6ezp OCHelMTKqtSi/Pii0pzU4kOMpkDPTWSWEk3OBya1vJJ4Q1NDcwtLQ3Njc2MzCyVx3g6BgzFC AumJJanZqakFqUUwfUwcnFINjBP0ZoqvvFqnv+FIxLrLR6OFHcN1rwTdnOzX5zrB1DyuYfJ7 MUWZ97vP7kiU7VA/cK/wtYheR8rURQ4x+QfW6kmrPtmxYj9DgOqPsG51GQmepY5KV14ZW/87 /PkNR9SjqFdGC1Y6Wq177rAmeInF1viLbUIcXOyhu1+eMVlW6+p6x/XeOZmd65VYijMSDbWY i4oTAaq2ugIyAwAA X-CMS-MailID: 20201012104640eucas1p12399708a49a999b779fdce7e9e6204cc X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20201009124900eucas1p26c93caa29c9925f1eef9be9ff7c6c65c X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20201009124900eucas1p26c93caa29c9925f1eef9be9ff7c6c65c References: <20201009075934.3509076-1-daniel.vetter@ffwll.ch> <20201009075934.3509076-10-daniel.vetter@ffwll.ch> <20201009123421.67a80d72@coco.lan> <20201009122111.GN5177@ziepe.ca> <20201009143723.45609bfb@coco.lan> <20201009124850.GP5177@ziepe.ca> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Jason, On 09.10.2020 14:48, Jason Gunthorpe wrote: > On Fri, Oct 09, 2020 at 02:37:23PM +0200, Mauro Carvalho Chehab wrote: > >> I'm not a mm/ expert, but, from what I understood from Daniel's patch >> description is that this is unsafe *only if* __GFP_MOVABLE is used. > No, it is unconditionally unsafe. The CMA movable mappings are > specific VMAs that will have bad issues here, but there are other > types too. I'm trying to follow this thread, but I really wonder what do you mean by CMA movable mappings? If a buffer has been allocated from CMA and used for DMA, it won't be moved in the memory. It will stay at the same physical memory address all the time until freed by the owner. It just a matter of proper usage count tracking to delay freeing if it is still used somewhere. Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland