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Tue, 4 Feb 2025 08:16:08 +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 hqYOI8jMoWepZwAAD6G6ig (envelope-from ); Tue, 04 Feb 2025 08:16:08 +0000 Message-ID: Date: Tue, 4 Feb 2025 09:16:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/3] mm: provide mapping_wrprotect_page() function To: Christoph Hellwig , Lorenzo Stoakes , Andrew Morton , Jaya Kumar , Simona Vetter , Helge Deller , linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , David Hildenbrand , Kajtar Zsolt , Maira Canal References: 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: D94934000C X-Stat-Signature: msy3mtdtfb56iq8dkfiqir5cw8t9ykjd X-HE-Tag: 1738656970-101297 X-HE-Meta: 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 ogxjkBX5 wX2uF7QHqI8HG6IxbsBZEj4YyS3kvgg8kiX+DTCZO6BG6XA7vxOVj1LT/WeSnUwMFF83dFT3TXKEpAjXAUA4TtWBu9TCB7C9Iqes2jY7sNu+Pfy8WJ67EbRJTf0xytph0uMgmU4R7wwPvLnIagWTYo/TiLSBKxvOt5qEJUKvccaE/lVeIbXuPeylHzINRsgosm7RZ1ZFkXtNfhduw8OaWNKz6IF8HZzYdlCRr/f47l8e4qP7/YhavTmU7+pLJAX3TMQTmd7OrDfm2thj0wlqtHeOScLTTdO1ipcH36DAbWexyg+/fhiXuzNIiSgHa1JHksFRVTe3PwbwsKviZXVFPK9/ISxtTzB72Nsj8amCi36tjwDl7w5QK+zPCZo1Tabe+4ARshsJBFLy6W/Vtu93cXLlhZ0OD6ZYjMO8Ap8B4OJt1e6s= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Am 04.02.25 um 06:36 schrieb Christoph Hellwig: > Hi Simona, > > > On Mon, Feb 03, 2025 at 04:49:34PM +0100, Simona Vetter wrote: >> Could we go one step further and entirely drop the struct page? Similar to >> unmap_mapping_range for VM_SPECIAL mappings, except it only updates the >> write protection. The reason is that ideally we'd like fbdev defio to >> entirely get rid of any struct page usage, because with some dma_alloc() >> memory regions there's simply no struct page for them (it's a carveout). > Umm, for dma_alloc* where * is not _pages you never can get a page or > PFN form them. They are block boxes and drivers must not attempt to > translated them into either a page or PFN or things will go wrong. > Only the kernel virtual address and dma_address may be used. > >> See e.g. Sa498d4d06d6 ("drm/fbdev-dma: Only install deferred I/O if >> necessary") for some of the pain this has caused. > The commit hash is corrupted, I guess this is 5a498d4d06d6 as the > subject line matches. And that commit (just like the code it is trying > to fix) is completely broken as it violates the above. As the author of these commits, I have no doubt that the code would break on some systems. It works in practice for the current use cases though. Is it possible to create something that tracks framebuffer writes without requiring pages? Best regards Thomas > > -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)