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Date: Sun, 15 Feb 2026 19:47:19 +0200
From: Mike Rapoport <rppt@kernel.org>
To: Peter Xu <peterx@redhat.com>
Cc: linux-mm@kvack.org, Andrea Arcangeli <aarcange@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Axel Rasmussen <axelrasmussen@google.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	David Hildenbrand <david@redhat.com>,
	Hugh Dickins <hughd@google.com>,
	James Houghton <jthoughton@google.com>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
	Michal Hocko <mhocko@suse.com>, Muchun Song <muchun.song@linux.dev>,
	Nikita Kalyazin <kalyazin@amazon.com>,
	Oscar Salvador <osalvador@suse.de>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Shuah Khan <shuah@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Vlastimil Babka <vbabka@suse.cz>, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH RFC 07/17] userfaultfd: introduce vm_uffd_ops
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On Wed, Feb 11, 2026 at 02:35:23PM -0500, Peter Xu wrote:
> On Sun, Feb 08, 2026 at 12:13:45PM +0200, Mike Rapoport wrote:
> > > 
> > > I understand you wanted to also make anon to be a driver, so this line
> > > won't apply to anon.  However IMHO anon is special enough so we can still
> > > make this in the generic path.
> > 
> > Well, the idea is to drop all vma_is*() in can_userfault(). And maybe
> > eventually in entire mm/userfaultfd.c
> > 
> > If all page cache filesystems need this, something like this should work,
> > right?
> > 
> > 	if (!uffd_supports_wp_marker() && (vma->vm_flags & VM_SHARED) &&
> > 	    (vm_flags & VM_UFFD_WP))
> > 		return false;
> 
> Sorry for a late response.
> 
> IMHO using vma_is_anonymous() for one more time should be better than
> leaking pte marker whole concept to modules. So the driver should only
> report if the driver supports UFFD_WP in general.  It shouldn't care about
> anything the core mm would already do otherwise, including this one on
> "whether system config / arch has globally enabled pte markers" and the
> relation between that config and the WP feature impl details.

I agree. Will move the check for the markers back into userfaultfd.c
 
> Thanks,
> 
> -- 
> Peter Xu
> 

-- 
Sincerely yours,
Mike.