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[209.85.208.170]) by smtp.gmail.com with ESMTPSA id p3-20020a2e7403000000b002770e6c620bsm1500123ljc.106.2022.11.07.20.52.53 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Nov 2022 20:52:53 -0800 (PST) Received: by mail-lj1-f170.google.com with SMTP id d3so19395788ljl.1 for ; Mon, 07 Nov 2022 20:52:53 -0800 (PST) X-Received: by 2002:a17:906:ee8e:b0:730:3646:d178 with SMTP id wt14-20020a170906ee8e00b007303646d178mr51989213ejb.426.1667882769115; Mon, 07 Nov 2022 20:46:09 -0800 (PST) MIME-Version: 1.0 References: <20221107161740.144456-1-david@redhat.com> <20221107161740.144456-17-david@redhat.com> In-Reply-To: <20221107161740.144456-17-david@redhat.com> From: Tomasz Figa Date: Tue, 8 Nov 2022 13:45:57 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH RFC 16/19] mm/frame-vector: remove FOLL_FORCE usage To: David Hildenbrand , Hans Verkuil , Marek Szyprowski Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, etnaviv@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, linux-kselftest@vger.kernel.org, Linus Torvalds , Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu , Greg Kroah-Hartman , Andrea Arcangeli , Hugh Dickins , Nadav Amit , Vlastimil Babka , Matthew Wilcox , Mike Kravetz , Muchun Song , Lucas Stach , David Airlie , Oded Gabbay , Arnd Bergmann , Mauro Carvalho Chehab Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi David, On Tue, Nov 8, 2022 at 1:19 AM David Hildenbrand wrote: > > FOLL_FORCE is really only for debugger access. According to commit > 707947247e95 ("media: videobuf2-vmalloc: get_userptr: buffers are always > writable"), the pinned pages are always writable. Actually that patch is only a workaround to temporarily disable support for read-only pages as they seemed to suffer from some corruption issues in the retrieved user pages. We expect to support read-only pages as hardware input after. That said, FOLL_FORCE doesn't sound like the right thing even in that case, but I don't know the background behind it being added here in the first place. +Hans Verkuil +Marek Szyprowski do you happen to remember anything about it? Best regards, Tomasz > > FOLL_FORCE in this case seems to be a legacy leftover. Let's just remove > it. > > Cc: Tomasz Figa > Cc: Marek Szyprowski > Cc: Mauro Carvalho Chehab > Signed-off-by: David Hildenbrand > --- > drivers/media/common/videobuf2/frame_vector.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c > index 542dde9d2609..062e98148c53 100644 > --- a/drivers/media/common/videobuf2/frame_vector.c > +++ b/drivers/media/common/videobuf2/frame_vector.c > @@ -50,7 +50,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > start = untagged_addr(start); > > ret = pin_user_pages_fast(start, nr_frames, > - FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM, > + FOLL_WRITE | FOLL_LONGTERM, > (struct page **)(vec->ptrs)); > if (ret > 0) { > vec->got_ref = true; > -- > 2.38.1 >