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Howlett" , Kyle Zeng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm/userfaultfd: only allocate anon_vma in CoW mappings Message-ID: References: <20261014-copy_hugetlb_page_range-v1-1-5b68e03fe7fe@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261014-copy_hugetlb_page_range-v1-1-5b68e03fe7fe@kernel.org> X-Rspamd-Queue-Id: C4B1940007 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: xzk7qkt5f5ggosure79sqoii1gctaaow X-HE-Tag: 1791989489-807384 X-HE-Meta: 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 AXEF7SCj DzafhdOBAmM9xxTPsFbsYNYd7rBiETp1AVMD3BFrTGRn6QlFzOxJ32UHYBs5BavcuWghQHOvsjRAG1BU4L4QKVTg0lsuGYqy+YQrnTa8BxNJ+9vD1N3d1MITVmyfn6jVKOOO5pY/j1FFnk+GzmxYqVz2WN6Ha8kwevnVzo2UsJUWx4l5yrjI6TCRww+QXc4hhli0/DxPnB5owjl8jzi+Oa226jzyWAchOfpgxxXQRIOelkgYA1nFzZpZlayx85fT2FTxcyb1S1dgpTksjQpg9L7uClFO7ycCz1gwRl7CWaxFUyGZ1bT1XWXXwp6kUNNBN6k8NNOOlm03EdlkbjenAnEb9Ig== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 14, 2026 at 01:53:11PM +0200, David Hildenbrand (Arm) wrote: > As uffd_lock_vma() is part of the same lookup machinery and > also contains a misleading VM_SHARED check, change that one as well > directly for consistency. OK, I think that one isn't _strictly necessary_, but while we're there, worth doing too, clearly. We should also go through and convert the remaining !VM_SHARED checks -> vma_is_cow_mapping() too if possible, but that's a follow up, obviously! > > A follow-up cleanup will stop taking the hugetlb_vma_lock_read(src_vma) > lock in copy_hugetlb_page_range() entirely. Further, the usage of Hmm really? Is it possible to do that without the hugetlb lock? It'd be good in general if we could get rid of that lock as a whole :) but maybe dreaming. > VM_SHARED in userfaultfd code should be cleaned up later to focus on > CoW vs. non-CoW mappings. I think also anywhere else in the kernel where this is done. An audit on that in general would be useful! > > Reported-by: Kyle Zeng > Fixes: 867a43a34ff8a ("userfaultfd: use per-vma locks in userfaultfd operations") > Cc: stable@vger.kernel.org > Signed-off-by: David Hildenbrand (Arm) This LGTM, thanks for handling this! Reviewed-by: Lorenzo Stoakes (ARM) -- Cheers, Lorenzo