| Message ID | 20201009075934.3509076-6-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | follow_pfn and other iomap races | expand |
On 10/9/20 12:59 AM, Daniel Vetter wrote: ... > @@ -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) { None of the callers that we have today will accept anything less than ret == nr_frames. And the whole partially pinned region idea turns out to be just not useful for almost everyone, from what I recall of the gup/pup call sites. So I wonder if we should just have get_vaddr_frames do the cleanup here and return -EFAULT, if ret != nr_frames ? thanks,
On Fri, Oct 16, 2020 at 9:54 AM John Hubbard <jhubbard@nvidia.com> wrote: > > On 10/9/20 12:59 AM, Daniel Vetter wrote: > ... > > @@ -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) { > > None of the callers that we have today will accept anything less than > ret == nr_frames. And the whole partially pinned region idea turns out > to be just not useful for almost everyone, from what I recall of the gup/pup > call sites. So I wonder if we should just have get_vaddr_frames do the > cleanup here and return -EFAULT, if ret != nr_frames ? Yeah I noticed that the calling convention here is a bit funny. But I with these frame-vector helpers now being part of drivers/media it's up to media folks if they want to clean that up, or leave it as is. If this would be in drm I'd say we'll have the loud warning and tainting due to CONFIG_STRICT_FOLLOW_PFN=n for 2-3 years. Then assuming no big complaints showed up, rip it all out and just directly call pup in each place that wants it (like I've done for habanalabs and exynos). -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
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); - goto out; + goto out_unlocked; } + 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)
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 <daniel.vetter@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Pawel Osciak <pawel@osciak.com> Cc: Marek Szyprowski <m.szyprowski@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Tomasz Figa <tfiga@chromium.org> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: Jan Kara <jack@suse.cz> Cc: Dan Williams <dan.j.williams@intel.com> 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 -- v2: Streamline the code and further simplify the loop checks (Jason) --- mm/frame_vector.c | 50 ++++++++++++++--------------------------------- 1 file changed, 15 insertions(+), 35 deletions(-)