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charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: DDA25180034 X-Stat-Signature: pmi8fjgzxhhne64rn91qn6x57igtcw57 X-HE-Tag: 1741014129-901172 X-HE-Meta: U2FsdGVkX1+pAcTEksyeu0jVUR1nZSCtbL2frJ2zX1GYvrEaWfzGmj2EzBYyiXdGxwgAnCZDQzLrxfEZK3rVIXXhv/Glp8eY6KiV0bq5Oq/nVO41QH4JqNn47rq4soXlDxPHdSGn5hRjY/ZDFtPZ7Pg2mrdQiJHfRBxl1lKyzQXbV3y8j7MHsAmab7SLqvkvwbNiR6XrBGLM4JBWHWoaznpTVuLAy/xz0ExLZ6M10oej/UpxE+nCNwO8MyY/gu1shLCvswt4xUGhDCYlqShrY/BURdHUicvFnx7ByV979ibIdR7W/UD7SmOJctCbiRTEKjKuBYniaSsGYPCXNP/qJCYLmgwADdKrC8wyY8h/oxOjh3l5GFhM14NfpfARiiTuQnOybfECe7hlDmizRCBD1d232goFFhlgj55sR8IzjpuNwW2vrAGUTXdjY1osFfYH8QZzXFsLSq0YScqxUs2OvHu4k+kwXWDXGYbGZLJPEZWTpIxHFqcP7HcKsLA4V+ayC7v+RHq4Tp0rlC3AGlRnHyd8yadcda2lyt6jnDWcRX6dzIiDcnkupdvArdAj5xRoDhgnp/lGYVWlLogq26LzisXUNvsYafKOuRGoWrZMT7EMPuqv3y0I8Oy4QadY6jfLJhKOe0Cn1MO9DmnNQuqNqvZ4hdoRjETrh4WjpZWlVSpajhklhPK39FhCl3vbyGUXwaxb2LqDwUQu7XddIcOWFCG1fQVPj0eaoyqTbf6uAIPLsOdyCE/W8JIDYM/kCTeRhEMCWRwQp1P2WrwT+l+nIb0ORFK2XQpH+Mxj+RasN7fe+5poh6JHb9lOFW5JVdOwNASVm6eY/Nf+JZR47UnVIzUN4+icG1fG+UerX0LQXjnOFZPRQBpuTfINeTzfpBzIwXcoDp6sqWcVM8DNQo4FDctrHxzJ/6dbboAsEvfZYnfwwZNlHKv1hPnfFdrkBvx3oPbPKfy3JUb5+6T/nKk DKdTS8HG zZzl8sXzl0JNiKF86e2JnyNv8iHiiDLtFPfG5q5DXlrKuKfZD66sE+5p2z/RXGvNpLcFTomHNt7GimCn54O5BZZUJEwve4YYa5FLtI9hU5uZyKsobaRgXDnfTtehPYBIjuUVkrsGE0c7F581+G/M3oY29QrT5i0Cz8OazKxP8HawSGm/viK1B5RCtpaIXnnNE8dANpYVBoMGGxWErkAY21tzYDVOjWu+BgkI36qCX0Gy1zifr4+UHcDXQrHNJsAUjPgnO7t76aHRbWLWp56cLakHFxPO4lADOQvN+hIB5Mjsanu/p21poAveL8mTuwuAG6IfRUP7xLj0phLw= 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 Sat, Mar 01, 2025 at 10:44:22AM -0500, Mathieu Desnoyers wrote: > > > Also, I notice that do_wp_page() only calls handle_userfault > > > VM_UFFD_WP when vm_fault flags does not have FAULT_FLAG_UNSHARE > > > set. > > > > AFAICT that's expected, unshare should only be set on reads, never writes. > > So uffd-wp shouldn't trap any of those. > > I'm confused by your comment. I thought unshare only applies to > *write* faults. What am I missing ? The major path so far to set unshare is here in GUP (ignoring two corner cases used in either s390 and ksm): if (unshare) { fault_flags |= FAULT_FLAG_UNSHARE; /* FAULT_FLAG_WRITE and FAULT_FLAG_UNSHARE are incompatible */ VM_BUG_ON(fault_flags & FAULT_FLAG_WRITE); } See the VM_BUG_ON() - if it's write it'll crash already. "unshare", in its earliest form of patch, used to be called COR (Copy-On-Read), which might be more straightforward in this case.. so it's the counterpart of COW but for read cases where a copy is required. The patchset that introduced it has more information (e.g. a7f2266041). Thanks, -- Peter Xu