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[34.76.131.216]) by smtp.gmail.com with ESMTPSA id f17sm23103391wme.22.2020.10.26.15.15.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Oct 2020 15:15:21 -0700 (PDT) Date: Mon, 26 Oct 2020 22:15:20 +0000 From: Tomasz Figa To: Daniel Vetter Cc: 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 , Jason Gunthorpe , Pawel Osciak , Marek Szyprowski , Kyungmin Park , Mauro Carvalho Chehab , Andrew Morton , John Hubbard , =?iso-8859-1?B?Suly9G1l?= Glisse , Jan Kara , Dan Williams Subject: Re: [PATCH v4 05/15] mm/frame-vector: Use FOLL_LONGTERM Message-ID: <20201026221520.GC2802004@chromium.org> References: <20201026105818.2585306-1-daniel.vetter@ffwll.ch> <20201026105818.2585306-6-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20201026105818.2585306-6-daniel.vetter@ffwll.ch> Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Hi Daniel, On Mon, Oct 26, 2020 at 11:58:08AM +0100, Daniel Vetter wrote: > This is used by media/videbuf2 for persistent dma mappings, not just > for a single dma operation and then freed again, so needs > FOLL_LONGTERM. > > Unfortunately current pup_locked doesn't support FOLL_LONGTERM due to > locking issues. Rework the code to pull the pup path out from the > mmap_sem critical section as suggested by Jason. > > By relying entirely on the vma checks in pin_user_pages and follow_pfn > (for vm_flags and vma_is_fsdax) we can also streamline the code a lot. > > Signed-off-by: Daniel Vetter > Cc: Jason Gunthorpe > Cc: Pawel Osciak > Cc: Marek Szyprowski > Cc: Kyungmin Park > Cc: Tomasz Figa > Cc: Mauro Carvalho Chehab > Cc: Andrew Morton > Cc: John Hubbard > Cc: Jérôme Glisse > Cc: Jan Kara > Cc: Dan Williams > Cc: linux-mm@kvack.org > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-samsung-soc@vger.kernel.org > Cc: linux-media@vger.kernel.org > Signed-off-by: Daniel Vetter > -- > v2: Streamline the code and further simplify the loop checks (Jason) > --- > mm/frame_vector.c | 50 ++++++++++++++--------------------------------- > 1 file changed, 15 insertions(+), 35 deletions(-) > Thank you for the patch. Please see my comments inline. > diff --git a/mm/frame_vector.c b/mm/frame_vector.c > index 10f82d5643b6..d44779e56313 100644 > --- a/mm/frame_vector.c > +++ b/mm/frame_vector.c > @@ -38,7 +38,6 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > struct vm_area_struct *vma; > int ret = 0; > int err; > - int locked; > > if (nr_frames == 0) > return 0; > @@ -48,40 +47,25 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > > start = untagged_addr(start); > > - mmap_read_lock(mm); > - locked = 1; > - vma = find_vma_intersection(mm, start, start + 1); > - if (!vma) { > - ret = -EFAULT; > - goto out; > - } > - > - /* > - * While get_vaddr_frames() could be used for transient (kernel > - * controlled lifetime) pinning of memory pages all current > - * users establish long term (userspace controlled lifetime) > - * page pinning. Treat get_vaddr_frames() like > - * get_user_pages_longterm() and disallow it for filesystem-dax > - * mappings. > - */ > - if (vma_is_fsdax(vma)) { > - ret = -EOPNOTSUPP; > - goto out; > - } > - > - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) { > + ret = pin_user_pages_fast(start, nr_frames, > + FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM, > + (struct page **)(vec->ptrs)); > + if (ret > 0) { > vec->got_ref = true; > vec->is_pfns = false; > - ret = pin_user_pages_locked(start, nr_frames, > - gup_flags, (struct page **)(vec->ptrs), &locked); Should we drop the gup_flags argument, since it's ignored now? > - goto out; > + goto out_unlocked; > } > Should we initialize ret with 0 here, since pin_user_pages_fast() can return a negative error code, but below we use it as a counter for the looked up frames? Best regards, Tomasz > + mmap_read_lock(mm); > vec->got_ref = false; > vec->is_pfns = true; > do { > unsigned long *nums = frame_vector_pfns(vec); > > + vma = find_vma_intersection(mm, start, start + 1); > + if (!vma) > + break; > + > while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) { > err = follow_pfn(vma, start, &nums[ret]); > if (err) { > @@ -92,17 +76,13 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > start += PAGE_SIZE; > ret++; > } > - /* > - * We stop if we have enough pages or if VMA doesn't completely > - * cover the tail page. > - */ > - if (ret >= nr_frames || start < vma->vm_end) > + /* Bail out if VMA doesn't completely cover the tail page. */ > + if (start < vma->vm_end) > break; > - vma = find_vma_intersection(mm, start, start + 1); > - } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP)); > + } while (ret < nr_frames); > out: > - if (locked) > - mmap_read_unlock(mm); > + mmap_read_unlock(mm); > +out_unlocked: > if (!ret) > ret = -EFAULT; > if (ret > 0) > -- > 2.28.0 >