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Tue, 3 Jun 2025 06:25:25 +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 f/MgCFWVPmi1egAAD6G6ig (envelope-from ); Tue, 03 Jun 2025 06:25:25 +0000 Message-ID: Date: Tue, 3 Jun 2025 08:25:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/4] fbdev/deferred-io: Support contiguous kernel memory framebuffers To: Michael Kelley , David Hildenbrand , "simona@ffwll.ch" , "deller@gmx.de" , "haiyangz@microsoft.com" , "kys@microsoft.com" , "wei.liu@kernel.org" , "decui@microsoft.com" , "akpm@linux-foundation.org" Cc: "weh@microsoft.com" , "hch@lst.de" , "dri-devel@lists.freedesktop.org" , "linux-fbdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-hyperv@vger.kernel.org" , "linux-mm@kvack.org" References: <20250523161522.409504-1-mhklinux@outlook.com> <20250523161522.409504-4-mhklinux@outlook.com> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 87F81A0009 X-Stat-Signature: 58iypyuj8k1dhyanbad3afbzgw5ctwaf X-Rspam-User: X-HE-Tag: 1748931927-544950 X-HE-Meta: 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 iN0Zg1QY 7lsRSF+GmXof5l5AR7guB94Q2338FP8PH5UuSUdU2O/ESiZnRSJDN7owoj4bbU3DzMm7Akw64DxVd8g/AaFD3sa0q89oK9ro04r8GonUhNYk2rHDkuzvVMNQ8Qu0oa3LhrC5g6dP+fndQCukxJTFUDiU5Fno04+V6OFMvJyTe869oXvHZwX8qtGjBzWKjjgy6f74ovHwX2KtLUvOpOGXuSiYKVsIr/7RJenyoqYgz3L91O0Wjiwpl+rRsjHoZ06hpSAtugQ3ikxBi87QNSqSDBAxSQYTCJ/zKUYF7dcugd5WWeHahdTeh9DcsNNIp8GhKvVbknL3EhstuyuxkyvJzu8Yv52jn+TNcu+CU X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 03.06.25 um 03:49 schrieb Michael Kelley: [...] >> Will the VMA have VM_PFNMAP or VM_MIXEDMAP set? PFN_SPECIAL is a >> horrible hack. >> >> In another thread, you mention that you use PFN_SPECIAL to bypass the >> check in vm_mixed_ok(), so VM_MIXEDMAP is likely not set? > The VMA has VM_PFNMAP set, not VM_MIXEDMAP. It seemed like > VM_MIXEDMAP is somewhat of a superset of VM_PFNMAP, but maybe that's > a wrong impression. vm_mixed_ok() does a thorough job of validating the > use of __vm_insert_mixed(), and since what I did was allowed, I thought > perhaps it was OK. Your feedback has set me straight, and that's what I > needed. :-) > > But the whole approach is moot with Alistair Popple's patch set that > eliminates pfn_t. Is there an existing mm API that will do mkwrite on a > special PTE in a VM_PFNMAP VMA? I didn't see one, but maybe I missed > it. If there's not one, I'll take a crack at adding it in the next version of my > patch set. What is the motivation behind this work? The driver or fbdev as a whole does not have much of a future anyway. I'd like to suggest removing hyperv_fb entirely in favor of hypervdrm? Best regards Thomas > > Michael -- -- 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)