From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E3205E81BDA for ; Mon, 9 Feb 2026 15:36:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 51B9F6B0096; Mon, 9 Feb 2026 10:36:01 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4C9B96B0099; Mon, 9 Feb 2026 10:36:01 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 381396B009B; Mon, 9 Feb 2026 10:36:01 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 1DF806B0096 for ; Mon, 9 Feb 2026 10:36:01 -0500 (EST) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id C5BB31A019D for ; Mon, 9 Feb 2026 15:36:00 +0000 (UTC) X-FDA: 84425318880.02.4196C7E Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf24.hostedemail.com (Postfix) with ESMTP id 2AA0E180012 for ; Mon, 9 Feb 2026 15:35:59 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=bhdTqqEF; spf=pass (imf24.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1770651359; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=SqkJV2sXP1wRLkW/07fo+sqhDpXMaIeJSZ+7lqVJnvw=; b=iWguKq7kcdVwfk2v36++h47/VBXgO1GolamMz4Yan6cLwF7QL9eeJprCIeDUXRswpEO1zt MLFt6DR4WtcL2YwxshOcIwJCgMlbPxJMClM39pDIFor2Kndz4p8nJ8lx0VHgeSbAT+4Yc9 lfRQZmOJ4j3T1OkSVjbkv9XiqsjBRwg= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=bhdTqqEF; spf=pass (imf24.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770651359; a=rsa-sha256; cv=none; b=RJW8UjssmhSjTxOpxq4FZY5uK+VV9erf1LFNVZZNuCsRpW7n8ZDmaw54qpnkFlc9PqOhAH udHzskUn58orBr0SjAsAr/0Qt5YS9ZNPjaJJxKByJe3sHcDNdR1hZkVU5GdM2MAsgJSjKl NnXWYw84ULUM9rMeEMeXLgnRjNHouoQ= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 7AB7A600CB; Mon, 9 Feb 2026 15:35:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 27CBAC116C6; Mon, 9 Feb 2026 15:35:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770651358; bh=zFz8vUni6pgix6F/mutd/GIOhr7EcTWq5cAQdEFI/3s=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=bhdTqqEFW/U2l1XAl5cmDWF9FoZVPME8mARaXEKe5Fxm78q0HCbx9NPbRB/5kgWdW bg8dINgqRpeLag95c4uljAKU/ydNCrNLWXXVTuSQH6CYGOrVgPnCd8BY9jV6Qedt3n wNFJ0LM1AK8jnnGABCJx25CtgCSuaY6oubiocc8VskI3BnFNsBWBRKTx6lzwlS6fcc Y8h6FOpXIDKszS5Ces6ZHEOZUweyoW7EDqwozSsM+6hMKRzBSjZNeO1OYARgkAMDxx /0mZq+gunlTDqcUAo8XXdhTmnjUhbLyGSam1gMxwnHpQIVSzPtEeTSF+mARMfv9/gf BKtgoYrV/UdGw== Message-ID: <0032ac8b-06ba-4f4b-ad66-f0195eea1c15@kernel.org> Date: Mon, 9 Feb 2026 16:35:47 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 00/17] mm, kvm: allow uffd suppot in guest_memfd To: Peter Xu , Mike Rapoport Cc: linux-mm@kvack.org, Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260127192936.1250096-1-rppt@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Stat-Signature: mzk47kztaz7qp46wsaunp9nsi669h73e X-Rspam-User: X-Rspamd-Queue-Id: 2AA0E180012 X-HE-Tag: 1770651359-798480 X-HE-Meta: U2FsdGVkX1/sPPGWzRylbDwUE9X4dix84l044579q4x50+5go6fCvZt9U/FoH4j0h3kDJDvnL8cZNBjnxPQ70aRDyml05QNIafdSz7jBtzMcI7VtNpcGa/CJwY6Vi1nBit82+mXGqgdmHsRNbpWcEvgXrSFaGdWqGIMz6DY+gwzocfaJFE8NbVUUHFUm0+qxg4Og/GjUv4FT1nnFH1B0N3zs24HdQal27rMJQQZVgi1OaVME89eEFkQtSbGXaHs2iyMmBmhyzOpbeDDWT0vCybtw86WGT8uR37jEfXtAXAxf/PDDy8TEUTH6N+G082j+pCyBEEO8wLl/KCj/N14txok6LOoK98+wl4igPl4FYrmXtDFG1U95jGzTsL4e5whgSnTps0KoHMiQTuuCCcjH2HN7Fai1jMxG3X4WNhOuNYiGxBF6qF3IC1Nvq7Jj2netK84HoY+TVKtTwpyD5CT8OcMv6yDZbcUoknxxThvsY4dribdTZW4nEWY3QgcEALZSd29QH3t+T2Fce0WthHubJkSOyKkPOa5+4ZCBbtOmd2GNQfcIMQGvVcQGFlmKTUjNnK12kniOgTlUYr8vVq0BS7+q+puFqGu5s/CYHUHYHjM6+z9uIrnOxxay+pP9VOsAt43pEYc+lnbbKD/xCF6wmHhHi/oELEDgE4nXyPFK8FuwWnG0ca+ZFsF7q/8DUxK8yUkeVpo5ZFq6EG0C+DeGy5cgBHcHSRftRZgCtvuLfjJsBkQplpH+6olRYhGMLcDgJmdC4iO4l5egHGdSIr+a8aCMAqyujAbRikykxgHBcWHD7r8FsAo98MJ3d+zrVZJ2r9QyjXJgj56ynqzfw9TM1TBB2iXyt/09L8J9g3hgmt5qzj2nhkSoLWxOqGD6lTQdVxkYrAJ81yHnEOCjAFCGKw+RlrZUzoTzgfPEykokvLzXAqIhxYkMqJRPzhAf4j6WllOGN3rIhcWIRih0SfR 07OLHC5R Wt0ngJMWNf9+eluo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/3/26 21:56, Peter Xu wrote: > On Tue, Jan 27, 2026 at 09:29:19PM +0200, Mike Rapoport wrote: >> From: "Mike Rapoport (Microsoft)" >> >> Hi, >> >> These patches enable support for userfaultfd in guest_memfd. >> They are quite different from the latest posting [1] so I'm restarting the >> versioning. As there was a lot of tension around the topic, this is an RFC >> to get some feedback and see how we can move forward. >> >> As the ground work I refactored userfaultfd handling of PTE-based memory types >> (anonymous and shmem) and converted them to use vm_uffd_ops for allocating a >> folio or getting an existing folio from the page cache. shmem also implements >> callbacks that add a folio to the page cache after the data passed in >> UFFDIO_COPY was copied and remove the folio from the page cache if page table >> update fails. >> >> In order for guest_memfd to notify userspace about page faults, there are new >> VM_FAULT_UFFD_MINOR and VM_FAULT_UFFD_MISSING that a ->fault() handler can >> return to inform the page fault handler that it needs to call >> handle_userfault() to complete the fault. >> >> Nikita helped to plumb these new goodies into guest_memfd and provided basic >> tests to verify that guest_memfd works with userfaultfd. >> >> I deliberately left hugetlb out, at least for the most part. >> hugetlb handles acquisition of VMA and more importantly establishing of parent >> page table entry differently than PTE-based memory types. This is a different >> abstraction level than what vm_uffd_ops provides and people objected to >> exposing such low level APIs as a part of VMA operations. >> >> Also, to enable uffd in guest_memfd refactoring of hugetlb is not needed and I >> prefer to delay it until the dust settles after the changes in this set. >> >> [1] https://lore.kernel.org/all/20251130111812.699259-1-rppt@kernel.org >> >> Mike Rapoport (Microsoft) (12): >> userfaultfd: introduce mfill_copy_folio_locked() helper >> userfaultfd: introduce struct mfill_state >> userfaultfd: introduce mfill_get_pmd() helper. >> userfaultfd: introduce mfill_get_vma() and mfill_put_vma() >> userfaultfd: retry copying with locks dropped in mfill_atomic_pte_copy() >> userfaultfd: move vma_can_userfault out of line >> userfaultfd: introduce vm_uffd_ops >> userfaultfd, shmem: use a VMA callback to handle UFFDIO_CONTINUE >> userfaultfd: introduce vm_uffd_ops->alloc_folio() >> shmem, userfaultfd: implement shmem uffd operations using vm_uffd_ops >> userfaultfd: mfill_atomic() remove retry logic >> mm: introduce VM_FAULT_UFFD_MINOR fault reason >> >> Nikita Kalyazin (5): >> mm: introduce VM_FAULT_UFFD_MISSING fault reason >> KVM: guest_memfd: implement userfaultfd minor mode >> KVM: guest_memfd: implement userfaultfd missing mode >> KVM: selftests: test userfaultfd minor for guest_memfd >> KVM: selftests: test userfaultfd missing for guest_memfd >> >> include/linux/mm.h | 5 + >> include/linux/mm_types.h | 15 +- >> include/linux/shmem_fs.h | 14 - >> include/linux/userfaultfd_k.h | 74 +- >> mm/hugetlb.c | 21 + >> mm/memory.c | 8 +- >> mm/shmem.c | 188 +++-- >> mm/userfaultfd.c | 671 ++++++++++-------- >> .../testing/selftests/kvm/guest_memfd_test.c | 191 +++++ >> virt/kvm/guest_memfd.c | 134 +++- >> 10 files changed, 871 insertions(+), 450 deletions(-) > > Mike, > > The idea looks good to me, thanks for this work! Your process on > UFFDIO_COPY over anon/shmem is nice to me. > > If you remember, I used to raise a concern on introducing two new fault > retvals only for userfaultfd: > > https://lore.kernel.org/all/aShb8J18BaRrsA-u@x1.local/ > > IMHO they're not only unnecessarily leaking userfaultfd information into > fault core definitions, but also cause code duplications. I still think we > should avoid them. > > This time, I've attached a smoke tested patch removing both of them. > > It's pretty small and it runs all fine with all old/new userfaultfd tests > (including gmem ones). Feel free to have a look at the end. > > I understand you want to avoid adding mnore complexity to this series, if > you want I can also prepare such a patch after this series landed to remove > the two retvals. I'd still would like to know how you think about it, > though, let me know if you have any comments. > > Note that it may indeed need some perf tests to make sure there's zero > overhead after this change. Currently there's still some trivial overheads > (e.g. unnecessary folio locks), but IIUC we can even avoid that. > > Thanks, > > ===8<=== > From 5379d084494b17281f3e5365104a7edbdbe53759 Mon Sep 17 00:00:00 2001 > From: Peter Xu > Date: Tue, 3 Feb 2026 15:07:58 -0500 > Subject: [PATCH] mm/userfaultfd: Remove two userfaultfd fault retvals > > They're not needed when with vm_uffd_ops. We can remove both of them. > Actually, another side benefit is drivers do not need to process > userfaultfd missing / minor faults anymore in the main fault handler. > > This patch will make get_folio_noalloc() required for either MISSING or > MINOR fault, but that's not a problem, as it should be lightweight and the > current only outside-mm user (gmem) will support both anyway. > > Signed-off-by: Peter Xu > --- > include/linux/mm_types.h | 15 +----------- > include/linux/userfaultfd_k.h | 2 +- > mm/memory.c | 45 +++++++++++++++++++++++++++++------ > mm/shmem.c | 12 ---------- > virt/kvm/guest_memfd.c | 20 ---------------- > 5 files changed, 40 insertions(+), 54 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index a6d32470a78a3..3cc8ae7228860 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -1612,10 +1612,6 @@ typedef __bitwise unsigned int vm_fault_t; > * fsync() to complete (for synchronous page faults > * in DAX) > * @VM_FAULT_COMPLETED: ->fault completed, meanwhile mmap lock released > - * @VM_FAULT_UFFD_MINOR: ->fault did not modify page tables and needs > - * handle_userfault(VM_UFFD_MINOR) to complete > - * @VM_FAULT_UFFD_MISSING: ->fault did not modify page tables and needs > - * handle_userfault(VM_UFFD_MISSING) to complete > * @VM_FAULT_HINDEX_MASK: mask HINDEX value > * > */ > @@ -1633,13 +1629,6 @@ enum vm_fault_reason { > VM_FAULT_DONE_COW = (__force vm_fault_t)0x001000, > VM_FAULT_NEEDDSYNC = (__force vm_fault_t)0x002000, > VM_FAULT_COMPLETED = (__force vm_fault_t)0x004000, > -#ifdef CONFIG_USERFAULTFD > - VM_FAULT_UFFD_MINOR = (__force vm_fault_t)0x008000, > - VM_FAULT_UFFD_MISSING = (__force vm_fault_t)0x010000, > -#else > - VM_FAULT_UFFD_MINOR = (__force vm_fault_t)0x000000, > - VM_FAULT_UFFD_MISSING = (__force vm_fault_t)0x000000, > -#endif > VM_FAULT_HINDEX_MASK = (__force vm_fault_t)0x0f0000, > }; > > @@ -1664,9 +1653,7 @@ enum vm_fault_reason { > { VM_FAULT_FALLBACK, "FALLBACK" }, \ > { VM_FAULT_DONE_COW, "DONE_COW" }, \ > { VM_FAULT_NEEDDSYNC, "NEEDDSYNC" }, \ > - { VM_FAULT_COMPLETED, "COMPLETED" }, \ > - { VM_FAULT_UFFD_MINOR, "UFFD_MINOR" }, \ > - { VM_FAULT_UFFD_MISSING, "UFFD_MISSING" } > + { VM_FAULT_COMPLETED, "COMPLETED" } > > struct vm_special_mapping { > const char *name; /* The name, e.g. "[vdso]". */ > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > index 75d5b09f2560c..5923e32de53b5 100644 > --- a/include/linux/userfaultfd_k.h > +++ b/include/linux/userfaultfd_k.h > @@ -85,7 +85,7 @@ struct vm_uffd_ops { > /* Checks if a VMA can support userfaultfd */ > bool (*can_userfault)(struct vm_area_struct *vma, vm_flags_t vm_flags); > /* > - * Called to resolve UFFDIO_CONTINUE request. > + * Required by any uffd driver for either MISSING or MINOR fault. > * Should return the folio found at pgoff in the VMA's pagecache if it > * exists or ERR_PTR otherwise. > * The returned folio is locked and with reference held. > diff --git a/mm/memory.c b/mm/memory.c > index 456344938c72b..098febb761acc 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5338,6 +5338,33 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) > return VM_FAULT_OOM; > } > > +static vm_fault_t fault_process_userfaultfd(struct vm_fault *vmf) > +{ > + struct vm_area_struct *vma = vmf->vma; > + struct inode *inode = file_inode(vma->vm_file); > + /* > + * NOTE: we could double check this hook present when > + * UFFDIO_REGISTER on MISSING or MINOR for a file driver. > + */ > + struct folio *folio = > + vma->vm_ops->uffd_ops->get_folio_noalloc(inode, vmf->pgoff); > + > + if (!IS_ERR_OR_NULL(folio)) { > + /* > + * TODO: provide a flag for get_folio_noalloc() to avoid > + * locking (or even the extra reference?) > + */ > + folio_unlock(folio); > + folio_put(folio); > + if (userfaultfd_minor(vma)) > + return handle_userfault(vmf, VM_UFFD_MINOR); > + } else { > + return handle_userfault(vmf, VM_UFFD_MISSING); > + } > + > + return 0; > +} > + > /* > * The mmap_lock must have been held on entry, and may have been > * released depending on flags and vma->vm_ops->fault() return value. > @@ -5370,16 +5397,20 @@ static vm_fault_t __do_fault(struct vm_fault *vmf) > return VM_FAULT_OOM; > } > > + /* > + * If this is an userfaultfd trap, process it in advance before > + * triggering the genuine fault handler. > + */ > + if (userfaultfd_missing(vma) || userfaultfd_minor(vma)) { > + ret = fault_process_userfaultfd(vmf); > + if (ret) > + return ret; > + } > + > ret = vma->vm_ops->fault(vmf); > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY | > - VM_FAULT_DONE_COW | VM_FAULT_UFFD_MINOR | > - VM_FAULT_UFFD_MISSING))) { > - if (ret & VM_FAULT_UFFD_MINOR) > - return handle_userfault(vmf, VM_UFFD_MINOR); > - if (ret & VM_FAULT_UFFD_MISSING) > - return handle_userfault(vmf, VM_UFFD_MISSING); > + VM_FAULT_DONE_COW))) > return ret; > - } > > folio = page_folio(vmf->page); > if (unlikely(PageHWPoison(vmf->page))) { > diff --git a/mm/shmem.c b/mm/shmem.c > index eafd7986fc2ec..5286f28b3e443 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2484,13 +2484,6 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index, > fault_mm = vma ? vma->vm_mm : NULL; > > folio = filemap_get_entry(inode->i_mapping, index); > - if (folio && vma && userfaultfd_minor(vma)) { > - if (!xa_is_value(folio)) > - folio_put(folio); > - *fault_type = VM_FAULT_UFFD_MINOR; > - return 0; > - } > - > if (xa_is_value(folio)) { > error = shmem_swapin_folio(inode, index, &folio, > sgp, gfp, vma, fault_type); > @@ -2535,11 +2528,6 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index, > * Fast cache lookup and swap lookup did not find it: allocate. > */ > > - if (vma && userfaultfd_missing(vma)) { > - *fault_type = VM_FAULT_UFFD_MISSING; > - return 0; > - } > - > /* Find hugepage orders that are allowed for anonymous shmem and tmpfs. */ > orders = shmem_allowable_huge_orders(inode, vma, index, write_end, false); > if (orders > 0) { > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 14cca057fc0ec..bd0de685f42f8 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -421,26 +421,6 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf) > folio = __filemap_get_folio(inode->i_mapping, vmf->pgoff, > FGP_LOCK | FGP_ACCESSED, 0); > > - if (userfaultfd_armed(vmf->vma)) { > - /* > - * If userfaultfd is registered in minor mode and a folio > - * exists, return VM_FAULT_UFFD_MINOR to trigger the > - * userfaultfd handler. > - */ > - if (userfaultfd_minor(vmf->vma) && !IS_ERR_OR_NULL(folio)) { > - ret = VM_FAULT_UFFD_MINOR; > - goto out_folio; > - } > - > - /* > - * Check if userfaultfd is registered in missing mode. If so, > - * check if a folio exists in the page cache. If not, return > - * VM_FAULT_UFFD_MISSING to trigger the userfaultfd handler. > - */ > - if (userfaultfd_missing(vmf->vma) && IS_ERR_OR_NULL(folio)) > - return VM_FAULT_UFFD_MISSING; > - } > - > /* folio not in the pagecache, try to allocate */ > if (IS_ERR(folio)) > folio = __kvm_gmem_folio_alloc(inode, vmf->pgoff); That looks better in general. We should likely find a better/more consistent name for fault_process_userfaultfd(). -- Cheers, David