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Mon, 30 Mar 2026 08:06:45 +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 PpdaIxUvymmnRwAAD6G6ig (envelope-from ); Mon, 30 Mar 2026 08:06:45 +0000 Message-ID: <1ed2d223-fcf2-46e3-8d5f-864440a49491@suse.de> Date: Mon, 30 Mar 2026 10:06:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm/shmem_helper: Make sure PMD entries get the writeable upgrade To: Boris Brezillon , Maarten Lankhorst , Maxime Ripard , dri-devel@lists.freedesktop.org Cc: David Airlie , Simona Vetter , linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , linux-mm@kvack.org, kernel@collabora.com, Biju Das , Tommaso Merciai References: <20260320151914.586945-1-boris.brezillon@collabora.com> 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: <20260320151914.586945-1-boris.brezillon@collabora.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: CCAAA1C0003 X-Stat-Signature: 91sfi1m3aiik78pk8eamft1n7isxcpxs X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1774858007-937386 X-HE-Meta: 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 lmD6/gBX 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Am 20.03.26 um 16:19 schrieb Boris Brezillon: > Unlike PTEs which are automatically upgraded to writeable entries if > .pfn_mkwrite() returns 0, the PMD upgrades go through .huge_fault(), > and we currently pretend to have handled the make-writeable request > even though we only ever map things read-only. Make sure we pass the > proper "write" info to vmf_insert_pfn_pmd() in that case. > > This also means we have to record the mkwrite event in the .huge_fault() > path now. Move the dirty tracking logic to a > drm_gem_shmem_record_mkwrite() helper so it can also be called from > drm_gem_shmem_pfn_mkwrite(). > > Note that this wasn't a problem before commit 28e3918179aa > ("drm/gem-shmem: Track folio accessed/dirty status in mmap"), because > the pgprot were not lowered to read-only before this commit (see the > vma_wants_writenotify() in vma_set_page_prot()). > > Fixes: 28e3918179aa ("drm/gem-shmem: Track folio accessed/dirty status in mmap") > Signed-off-by: Boris Brezillon > Cc: Biju Das > Cc: Thomas Zimmermann > Cc: Tommaso Merciai Acked-by: Thomas Zimmermann > --- > > This patch is based on drm-tip [2], because that's the only branch > that has both [1] and the dirty tracking changes that live in > drm-misc-next. > > Also added the THP maintainers in Cc, so I can hopefully get some > feedback on the fix. For instance, I'm still unsure > drm_gem_shmem_pfn_mkwrite() is race-free (do we need some locking > there? should we call folio_mark_dirty_lock()? should we call the > fault handler directly from there and have all the dirty tracking > in this .[huge_]fault path?). > > [1]https://yhbt.net/lore/dri-devel/20260319015224.46896-1-pedrodemargomes@gmail.com/ > [2]https://gitlab.freedesktop.org/drm/tip > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 46 ++++++++++++++++++-------- > 1 file changed, 32 insertions(+), 14 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index 2062ca607833..545933c7f712 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -554,6 +554,21 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev, > } > EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create); > > +static void drm_gem_shmem_record_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); > + loff_t num_pages = obj->size >> PAGE_SHIFT; > + pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within VMA */ > + > + if (drm_WARN_ON(obj->dev, !shmem->pages || page_offset >= num_pages)) > + return; > + > + file_update_time(vma->vm_file); > + folio_mark_dirty(page_folio(shmem->pages[page_offset])); > +} > + > static vm_fault_t try_insert_pfn(struct vm_fault *vmf, unsigned int order, > unsigned long pfn) > { > @@ -566,8 +581,23 @@ static vm_fault_t try_insert_pfn(struct vm_fault *vmf, unsigned int order, > > if (aligned && > folio_test_pmd_mappable(page_folio(pfn_to_page(pfn)))) { > + vm_fault_t ret; > + > pfn &= PMD_MASK >> PAGE_SHIFT; > - return vmf_insert_pfn_pmd(vmf, pfn, false); > + > + /* Unlike PTEs which are automatically upgraded to > + * writeable entries, the PMD upgrades go through > + * .huge_fault(). Make sure we pass the "write" info > + * along in that case. > + * This also means we have to record the write fault > + * here, instead of in .pfn_mkwrite(). > + */ > + ret = vmf_insert_pfn_pmd(vmf, pfn, > + vmf->flags & FAULT_FLAG_WRITE); > + if (ret == VM_FAULT_NOPAGE && (vmf->flags & FAULT_FLAG_WRITE)) > + drm_gem_shmem_record_mkwrite(vmf); > + > + return ret; > } > #endif > } > @@ -655,19 +685,7 @@ static void drm_gem_shmem_vm_close(struct vm_area_struct *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); > - loff_t num_pages = obj->size >> PAGE_SHIFT; > - pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within VMA */ > - > - if (drm_WARN_ON(obj->dev, !shmem->pages || page_offset >= num_pages)) > - return VM_FAULT_SIGBUS; > - > - file_update_time(vma->vm_file); > - > - folio_mark_dirty(page_folio(shmem->pages[page_offset])); > - > + drm_gem_shmem_record_mkwrite(vmf); > return 0; > } > -- -- 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)