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Wed, 25 Feb 2026 11:35:39 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id TmNoCovenmlwIAAAD6G6ig (envelope-from ); Wed, 25 Feb 2026 11:35:39 +0000 Message-ID: <788bd9a6-003a-4761-ab4c-1bc0cb716d9c@suse.de> Date: Wed, 25 Feb 2026 12:35:38 +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> <0d00a0f6-d0e4-41db-b48b-77157cd2e968@suse.de> <20260209160109.79a020ae@fedora> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Action: no action X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 1090140006 X-Stat-Signature: eamcjqfd7x1tnephhwc8u6z63z1coths X-HE-Tag: 1772019340-206709 X-HE-Meta: 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 0CsYBn0i jFHxxffDbO35VYx5my18Ql6bK3MwOzCquLgXkqgvFJc1EkGXWsxNC7xuuuw2dx5wNxSG51gfJBBSRtae3i1Wbkk8EFPH3pi24UWbECI0Chbo+LPxPxsBPWny2ctGi7zOvgAsgcPi3/rTRs0FOby4xZRq1pi+GxTpY0oXw6Qhq8Nvwdq83pYx3C6WSkB2O5Y59251OZqAYAxMtJXGD4A+xS4YhkgEWKbPw4SA+P7lLvBLqQv2XCj+TdiyDYFxWVyOujEvVx8jEF/x28DaguKRTa8IKg6G7GjGFLt0/b4yzL1aKcBCnkWjF4QsxwzwlRXUzJXx4EeSs0esCDcuGoogv54xUMDUHbmTN7N7RnvvLDwPswB+5lspQQARi7HOK/rbY4XApuGDa99wCDPwNoq/qe7h74Mh0L1rMEi6RT75F3rjUZryM6AeViTfhybVOoP5FfM18NbugT/guXjw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Am 09.02.26 um 16:01 schrieb Boris Brezillon: > On Mon, 9 Feb 2026 15:46:21 +0100 > Thomas Zimmermann wrote: > >> 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(). > I agree it's not supposed to happen, but isn't it what WARN_ON()s are > for (catching unexpected situations)? OK, with Frank's ack on the imagination changes in, I'll send out an update with additional warning. Best regards Thomas -- -- 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)