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b=Qpl6pTLoaAeBpcbEKuwh7r8MjAtDrlHX9jbAvcFpcR3CrHgdYxXx4sNdOyT+5UBKY hwZq5M/8DVldhkxcUcUBBVJpFFJx65vumAzWROkhZFaJiuN/Go9Oo5qBngNafk2Hnz 4Kxq6N+gG+DKLwsJ0rRHEZidN7GEYCsTMgChe8YBhRjImyKcBI3UrAtavVAVigyJLv z676QZZTMwHGh3tA/ERm62yiT+TLykLWSMuKPn3ZFlO4phL6vWjYq5HA7PXoJyoZ/A GP89f/3ADUV4wdxx07Q2m2351EcJIaNzyIUdQOg2KcUhJ+DF4PThf+Jgvs99hwVs8n TfuPMAbNrQQ5Q== Date: Mon, 24 Aug 2026 11:17:00 +0300 From: Mike Rapoport To: Lance Yang 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 Subject: Re: [PATCH 6/6] userfaultfd: collapse VM_UFFD_{MISSING,WP,MINOR,RWP} into single VM_UFFD Message-ID: References: <20260823-uffd-vm-flags-v1-v1-6-3086981b33cf@kernel.org> <20260824071126.41979-1-lance.yang@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260824071126.41979-1-lance.yang@linux.dev> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 6F7B920003 X-Stat-Signature: ocbcp48khmd5z8zdwnxzeeuwcqygbx8f X-Rspam-User: X-HE-Tag: 1787559434-463304 X-HE-Meta: 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 fkBMbNOs +o8kO/PEwaYdX6uDMyMQga5Jhhib7bEk0Cg2ED7IcRg2j6h1nGU+EIg8b4ApgoAXgkHXvi6KaUpiyXa3dJFAH4hDepp43OLhuTqCUtQI9aFoQnAQfc13ujTtCiVXGriXM3qOSya3zNIkBKKYQWH76fXZAw8tNjIwGk5HR6WT1HIXkvSq+w01J/JUw+sJsYb/zfE1GPeXkTVA/WlXykWin3On8MGVgTEwYFTUBV+UOmUaWsEkEh2fP1EZj4g3MnWiZX26q3BlxJwjdOo+yHgNBSlwij1oh1hYzvDM7jgDIfY+gEtk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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! > 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)) return true; /* VMA type or effective uffd_ops changed while the lock was dropped */ > Cheers, Lance -- Sincerely yours, Mike.