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Mon, 24 Aug 2026 08:28:00 +0000 X-Mizu-Trace-ID: 8e0a79e38506ea9a X-Migadu-Flow: FLOW_OUT Message-ID: Date: Mon, 24 Aug 2026 16:27:39 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6/6] userfaultfd: collapse VM_UFFD_{MISSING,WP,MINOR,RWP} into single VM_UFFD To: Mike Rapoport Cc: akpm@linux-foundation.org, david@kernel.org, baolin.wang@linux.alibaba.com, baohua@kernel.org, dev.jain@arm.com, hughd@google.com, jannh@google.com, jgg@ziepe.ca, jhubbard@nvidia.com, corbet@lwn.net, liam@infradead.org, ljs@kernel.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, mhocko@suse.com, muchun.song@linux.dev, nico.pache@linux.dev, osalvador@suse.de, pfalcato@suse.de, peterx@redhat.com, ryan.roberts@arm.com, shakeel.butt@linux.dev, skhan@linuxfoundation.org, rostedt@goodmis.org, surenb@google.com, usama.arif@linux.dev, vbabka@kernel.org, ziy@nvidia.com, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org References: <20260823-uffd-vm-flags-v1-v1-6-3086981b33cf@kernel.org> <20260824071126.41979-1-lance.yang@linux.dev> Content-Language: en-US From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 5BC2FC0007 X-Rspam-User: X-Stat-Signature: f9ij396fq48miipo9uqyn59q9mhnw7tk X-Rspamd-Server: rspam06 X-HE-Tag: 1787560082-613130 X-HE-Meta: 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 rqUA+oZK kd4UWnD7nZSi6tYbnTM9vIx1QE3322Swhy8aWquUzLCOMDGMhTCG89wmJsVxDRbeG1BSdaICWCFTHU/1JKbw2cwgI/OjtcZCYo/DUGHwFoO1nCeFWo93KOltWbxzru9wB4S2BrB2/C7PxH1aWllUhcsvWE5KmsiUfkvzx/w2ln+ppLb17DcJxx/TiyNLk7jUa3immgplrhVL9aw8YB3gQ4SLtciT9x/Rnc/lBunaaPAP541nXLvJrHaiqYwsiH66uKAPYT6kEf0LpyQxmFgqLu9cXvceB4PmZP428Ecibhm9hk8W+ac9VOfcowCXJObAYDTPE Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/8/24 16:17, Mike Rapoport wrote: > Hi Lance, > > On Mon, Aug 24, 2026 at 03:11:26PM +0800, Lance Yang wrote: >> >> On Sun, Aug 23, 2026 at 03:17:43PM +0300, Mike Rapoport (Microsoft) wrote: >> [...] >>> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c >>> index 83587d34b189..193f6e65d875 100644 >>> --- a/mm/userfaultfd.c >>> +++ b/mm/userfaultfd.c >>> @@ -50,10 +50,10 @@ struct mfill_state { >>> pmd_t *pmd; >>> }; >>> >>> -static bool anon_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags) >>> +static bool anon_can_userfault(struct vm_area_struct *vma, unsigned int mode) >>> { >>> /* anonymous memory does not support MINOR mode */ >>> - if (vm_flags & VM_UFFD_MINOR) >>> + if (mode & UFFD_MODE_MINOR) >>> return false; >>> return true; >>> } >>> @@ -462,7 +462,7 @@ static int mfill_copy_folio_locked(struct folio *folio, unsigned long src_addr) >>> } >>> >>> #define MFILL_RETRY_STATE_VMA_FLAGS \ >>> - append_vma_flags(__VMA_UFFD_FLAGS, VMA_SHARED_BIT) >>> + append_vma_flags(VMA_UFFD, VMA_SHARED_BIT) >> >> Looks like this drops registration mode from the retry snapshot. Assume a >> shared shmem VMA is registered for MISSING and COPY reaches >> mfill_copy_folio_retry(). While locks are dropped, the same userfaultfd| >> can re-register the range for MINOR. VMA_UFFD, VM_SHARED, ops, file and >> pgoff all stay unchanged, so the old COPY can continue instead of >> returning -EAGAIN ... no? > > Good catch, thanks! Cheers! > >> Maybe something like this? > > I prefer to add mode to the retry_state: > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 193f6e65d875..a0377f7ecc69 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -471,6 +471,7 @@ static int mfill_copy_folio_locked(struct folio *folio, unsigned long src_addr) > */ > struct mfill_retry_state { > const struct vm_uffd_ops *ops; > + unsigned long mode; > struct file *file; > vma_flags_t flags; > pgoff_t pgoff; > @@ -482,6 +483,7 @@ static void mfill_retry_state_save(struct mfill_retry_state *s, > s->flags = vma_flags_and_mask(&vma->flags, MFILL_RETRY_STATE_VMA_FLAGS); > s->ops = vma_uffd_ops(vma); > s->pgoff = vma_start_pgoff(vma); > + s->mode = uffd_mode(vma); > > if (vma->vm_file) > s->file = get_file(vma->vm_file); > @@ -493,8 +495,9 @@ static bool mfill_retry_state_changed(struct mfill_retry_state *state, > vma_flags_t flags = vma_flags_and_mask(&vma->flags, > MFILL_RETRY_STATE_VMA_FLAGS); > > - /* Have any UFFD flags (missing, WP, minor) changed? */ > - if (!vma_flags_same_pair(&state->flags, &flags)) > + /* UFFD registration mode or VMA sharing changed */ > + if (!vma_flags_same_pair(&state->flags, &flags) || > + s->mode != uffd_mode(vma)) I assume you meant s/s->mode/state->mode/ With that, LGTM :) > return true; > > /* VMA type or effective uffd_ops changed while the lock was dropped */ > >> Cheers, Lance > Cheers, Lance