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Wed, 14 Oct 2026 11:04:22 -0700 (PDT) Received: from com-75606 ([199.47.143.7]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-83039076dc3sm17027951a34.14.2026.10.14.11.04.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Oct 2026 11:04:21 -0700 (PDT) Date: Wed, 14 Oct 2026 11:04:17 -0700 From: Kyle Zeng To: "Lorenzo Stoakes (ARM)" Cc: "David Hildenbrand (Arm)" , Muchun Song , Oscar Salvador , Andrew Morton , Mike Rapoport , Peter Xu , Miaohe Lin , Lokesh Gidra , "Liam R. Howlett" , 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: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 27058100007 X-Rspam-User: X-Stat-Signature: xwmd5g934b6akdwzd13arbuueahes47d X-HE-Tag: 1792001063-704628 X-HE-Meta: U2FsdGVkX18BhNCd+aUFw9P7FlRKpNfH8fwTreUw212L7OQufjQaNmlkPUEJgyNe4uMOYobkF+I1jNwYuBTdGDgfUcrFCaRCsKjUg05Snqg+L0k1Lz/MjiQSYOCrXXUqcf2BXgmxs2QTid/RxW+Q8A8BGjGo9myhrnKYPPU72hdVKxw35DdP1zN97638Z+R3PRR/uMzVIrgPFqe/aRVPy5u1j5H4+xMoYqvCEzXL3vgz6B/bWCVHace2zLv19AyOpJXkyWJWnTaG5IwcNpix6VAivS3a0do9b48HC3LghzREHqm46Gs61gYAvmuL29uOswsR2hVzymJP6SQ1mK7JwucVrZEY4FhoGBDbp7S6HCGYf94hZ+p7BcxpgFNsTOwIPuIfd+YpBE5rkYgqUKQphbKVgXE5SqwMAtF23LwaIgellVfPyEb7HcrxHc3YUr983nU/WZhp7cwYAF6bOFMEF1ASM2MgrLuzz/PYLorlUlqlQu0XyoYeRO3DkWhNQB3yqbj6pqifnnOlUweyUxG22CWd5aI2NbI9pxtTdvTDp+Qh4PyKefh6GK90VJBX0hWyoJq4r/6E1wOsdcklgcG/cleKCqkYcj4XN4V23D5NP4+GzxezAGQI6mfnW8RGQq0FUSUNkXv2nZ8vUfoHRp2DYc64jtpJIRwQSZv0Pi+aNifDGb7fTYKtApzx+mBULH3T6dqpcI7qwm/6TLvlt18ymRS9qpJBiS55rM+7Hm3p/sXEOlJC144iADsZulOkpDFAG0/kREAWXMd/c3c4XEpqW/m4lpppVey9wFyvkONFDrQyjct/b+xhMZbTy8fAaHM13sjDbSctyJ0XYpHTjCofGUxp09kFB/qV0v8MqqacWTJ81QPB+heJouipxySuwkfpSHgZEOhHERa0zwqYD483yxIU3x3bRrw+DUgjVp6ngm0eI53FeGeKg72dI7mc3Iuqka5c/Tk//yjtYjLMlw5 POcGCG2k PX3tA8aym86HS7CbK67bEWTG3Go2eAyTCmVizlGmkG/n88uEccqnYo1PqpGEKChagbP9thN61FlD+W0q3qWiMWbcP5b7wLX6iGwAlxufH03hanBiU78yWG09H0wZ1K9K2CHDsOVRKcxR682sumkWO3kM/3BxHfTqWtZIiYqnkDUmdugFelLYgp0ai2ciDPvBRcGmhBnRO+kqllOIVIKiBfY0i2EHrytABEDuI2TW0TwKlzPe2QXXPsYUj/VA+1mEXu4sZ118jK801uD4AfqMOuSMauJ40px6fl1zVljohJ9x7pspG7acZgs7E1KY3m/p2S1QBTj/rZQOX1MyeA2D3hlOsqd1v0ttkXr1k5srgkdMuJqQPYW+FFnK0nJIzMTaJUSVTpEktKBgI8uN3wwOMt5qLcg== 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 03:51:22PM +0100, Lorenzo Stoakes (ARM) wrote: > 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 I ran the patch through my system and did not find any issues with this patch. Thanks for addressing this! Reviewed-by: Kyle Zeng