From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1B63B346E7A; Mon, 24 Aug 2026 08:17:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787559435; cv=none; b=JORIu3qqwkUjebGpa3RrOoXKqeaCvZfwZVczkEW+LFicZGK9VOAgBo7V6IZvYX7JM4XF3rnQxTAbt3HsQj+UpeOzzKh1cq4SS3/nOjlH9ERfK+Gq0d93zqPHR5fcGjv51+uXSpnthEPTuIFV6nY7q/cD8SRjqQT+tHra2KhTQgM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787559435; c=relaxed/simple; bh=l5DE0vLKC2aO/UHzn1eUKYSOSLzkqDEzUDKrM/QvHwE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ji206NvkeSBWidy/JWhzyRYbXxoITk8JMXhpPOskDVouZKFsAwEsrYQsTeW357IjFDXv2RN5bPKEM+ZqzEe2s++I6wzq2SGrkw0aMQLXnB/USpf8624kGFT0/sh4WamZXHgg31FUt/uk8SvCHJuFND3O15OuIIxTWOZ5GwkHvpQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Qpl6pTLo; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Qpl6pTLo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D8F411F000E9; Mon, 24 Aug 2026 08:17:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787559433; bh=IXaDWANMBlI65kh+v9rkRtQjLvm/PKZVB63CiqD6Ees=; h=Date:From:To:Cc:Subject:References:In-Reply-To; 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> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260824071126.41979-1-lance.yang@linux.dev> 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.