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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3D1E040014 X-Stat-Signature: 5acw9s8h4hh98xmjsf1wi13oahj3gxn5 X-Rspam-User: X-HE-Tag: 1750184745-799747 X-HE-Meta: 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 wTHmRbmM qUNuk2Ayg5m630pDOS0k3ZJlcdZ3ce/BNXiv6kbePtOOEwIDjjNa5VnbbedgPIuPAl3lq1n/TXHaG7RO4DEfznBBd7FJlL+EttrvJorlIRXn+qlr9FyMUfMxvx1Lbw1oTDhaLD3VV5c3h7/9VCe+0JlxseM3WxC8+xNWMePUQIojvxTsCXcN5uvqr/4Hkw4agpkEvfR49rx//dI/NmahYXKckZu+QOGvr6x1HEm7LaxJ4A3XiUZIkXuhktlmNugLkNwfmZXsJ0+n1ilSt3/DK2VBoYz++CXrHt1m9xuQez6s4QjlVjomc3KcXMoRe4ZKMn2IzMl/jAuv0lu8PxECeBVXnz6mTdKiWefziPX4Eyj3sMyrWFlrDM6eeeXk5775WcaXwv3ixArolM2GeBu7J4BcsED1wd8eOfcYawq4s48cOLuRf6fGLzxIXJ83Si1xrTX8p9bmafaHLA1U= 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: On 17.06.25 18:18, David Hildenbrand wrote: > On 17.06.25 17:43, David Hildenbrand wrote: >> RFC because it's based on mm-new where some things might still change >> around the devmap removal stuff. >> >> While removing support for CoW PFNMAPs is a noble goal, I am not even sure >> if we can remove said support for e.g., /dev/mem that easily. >> >> In the end, Cow PFNMAPs are pretty simple: everything is "special" except >> CoW'ed anon folios, that are "normal". >> >> The only complication is: how to identify such pages without pte_special(). >> Because with pte_special(), it's easy. >> >> Well, of course, one day all architectures might support pte_special() ... >> either because we added support for pte_special() or removed support for >> ... these architectures from Linux. >> >> No need to wait for that day. Let's do some cleanups around >> vm_normal_page()/vm_normal_page_pmd() and handling of the huge zero folio, >> and remove the "horrible special case to handle copy-on-write behaviour" >> that does questionable things in remap_pfn_range() with a VMA, simply by >> >> ... looking for anonymous folios in CoW PFNMAPs to identify anonymous >> folios? I know, sounds crazy ;) > > I'll mention one corner case that just occurred to me: assume someone > maps arbitrary /dev/mem that is actually used by the kernel for user > space, and then some of that memory gets allocated as anonymous memory, > it would probably be a problem. > > Hmm, I'll have to think about that, and the interaction with > CONFIG_STRICT_DEVMEM. The /dev/mem mapping of arbitrary memory is indeed the hard case. To handle all that, patch #11 is too simplistic. I have some idea how to make it work, but have to think about a couple of corner cases. -- Cheers, David / dhildenb