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Mon, 09 Feb 2026 14:46:22 +0000 Message-ID: <0d00a0f6-d0e4-41db-b48b-77157cd2e968@suse.de> Date: Mon, 9 Feb 2026 15:46:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 5/6] drm/gem-shmem: Track folio accessed/dirty status in mmap To: Boris Brezillon Cc: loic.molinari@collabora.com, willy@infradead.org, frank.binns@imgtec.com, matt.coster@imgtec.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org, airlied@gmail.com, simona@ffwll.ch, dri-devel@lists.freedesktop.org, linux-mm@kvack.org References: <20260209133241.238813-1-tzimmermann@suse.de> <20260209133241.238813-6-tzimmermann@suse.de> <20260209152340.16f9b30a@fedora> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: <20260209152340.16f9b30a@fedora> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[11]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[collabora.com,infradead.org,imgtec.com,linux.intel.com,kernel.org,gmail.com,ffwll.ch,lists.freedesktop.org,kvack.org]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,suse.de:mid,suse.de:dkim,suse.de:email,suse.com:url]; URIBL_BLOCKED(0.00)[suse.com:url,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,suse.de:mid,suse.de:dkim,suse.de:email,collabora.com:email]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Queue-Id: 8272F3E6E7 X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi Boris, thanks for reviewing the series. Am 09.02.26 um 15:23 schrieb Boris Brezillon: > On Mon, 9 Feb 2026 14:27:14 +0100 > Thomas Zimmermann wrote: > >> Invoke folio_mark_accessed() in mmap page faults to add the folio to >> the memory manager's LRU list. Userspace invokes mmap to get the memory >> for software rendering. Compositors do the same when creating the final >> on-screen image, so keeping the pages in LRU makes sense. Avoids paging >> out graphics buffers when under memory pressure. >> >> In pfn_mkwrite, further invoke the folio_mark_dirty() to add the folio >> for writeback should the underlying file be paged out from system memory. >> This rarely happens in practice, yet it would corrupt the buffer content. >> >> This has little effect on a system's hardware-accelerated rendering, which >> only mmaps for an initial setup of textures, meshes, shaders, etc. >> >> v3: >> - rewrite for VM_PFNMAP >> v2: >> - adapt to changes in drm_gem_shmem_try_mmap_pmd() >> >> Signed-off-by: Thomas Zimmermann >> Reviewed-by: Boris Brezillon >> --- >> drivers/gpu/drm/drm_gem_shmem_helper.c | 20 ++++++++++++++++++++ >> 1 file changed, 20 insertions(+) >> >> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c >> index c3a054899ba3..0c86ad40a049 100644 >> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c >> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c >> @@ -598,6 +598,9 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) >> if (ret != VM_FAULT_NOPAGE) >> ret = vmf_insert_pfn(vma, vmf->address, pfn); >> >> + if (likely(!(ret & VM_FAULT_ERROR))) > Can't we just go > > if (ret == VM_FAULT_NOPAGE) > > here? After reviewing the code in vmf_insert_pfn, I think so. All we'll see is _OOM and _SIGBUS; or _NOPAGE on success.  I'll change it then. > >> + folio_mark_accessed(folio); >> + >> out: >> dma_resv_unlock(obj->resv); >> >> @@ -638,10 +641,27 @@ static void drm_gem_shmem_vm_close(struct vm_area_struct *vma) >> drm_gem_vm_close(vma); >> } >> >> +static vm_fault_t drm_gem_shmem_pfn_mkwrite(struct vm_fault *vmf) >> +{ >> + struct vm_area_struct *vma = vmf->vma; >> + struct drm_gem_object *obj = vma->vm_private_data; >> + struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj); >> + pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within VMA */ >> + struct page *page = shmem->pages[page_offset]; > Should we have a > > if (WARN_ON(!shmem->pages || > page_offset <= (obj->size >> PAGE_SHIFT))) > return VM_FAULT_SIGBUS; > > > ? I left it out because it doesn't seem necessary.  In the fault handler in drm_gem_shmem_fault(), I can see that we could get an OOB access. But we only call pfn_mkwrite() after going through _fault() first. I don't see a way of getting here unless we've already tested for the page in _fault(). Best regards Thomas > >> + struct folio *folio = page_folio(page); >> + >> + file_update_time(vma->vm_file); >> + >> + folio_mark_dirty(folio); >> + >> + return 0; >> +} >> + >> const struct vm_operations_struct drm_gem_shmem_vm_ops = { >> .fault = drm_gem_shmem_fault, >> .open = drm_gem_shmem_vm_open, >> .close = drm_gem_shmem_vm_close, >> + .pfn_mkwrite = drm_gem_shmem_pfn_mkwrite, >> }; >> EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops); >> -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)