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 80C7443BDDE; Fri, 2 Oct 2026 07:48:58 +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=1790927340; cv=none; b=JKVJMKUbXz44jd7CA9lWGwBeOHFupJLHzLTRkmc0Z630WQph3tFTl/fc4lYamFhSXHlEaEEVDY2LdSVHIhHAkeB/5QRV2Hfc6rmBZopreeNuZG3CZV64J1H5z8fsyDD5ez/qngHg8fhr4GuhGz2HQORJtpB/722Fdg4juu4U0sw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790927340; c=relaxed/simple; bh=vRYMdLYcZqs9ZGif3rlg7KJTTJlkiCi7BTNpC4uiw4k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=k7HWCXxs4RYksffjp/A9iNqT0813W/sWyxxrfK1SyteRo+2ERsq73vtvtW9WMO+a9yaR/wM1B7ue6WVKs4cvtMRsPwPjM/sXsuKLFjMps2d6u6XEea9vbULiYB0lr30O5evvm2iaMkZxQxLj7E85E1XNxNiUG/68A80B72Ys4VA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=m/ZpHLuD; 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="m/ZpHLuD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7558F1F000FF; Fri, 2 Oct 2026 07:48:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790927338; bh=VuJQjhi77ZVm2icnOLnl3Y2tfYl+LAIPkt+sFQXlE00=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=m/ZpHLuDFIK1LoopTh4kNdvd7txlk1dEmXGio8sGjgBF+jhPpVEmgrx1I7J3QtPF9 mq6SLVvXjHAYq1lJ6wsRrm6oIMjx3WZJY2lu4n7AgTKI3GT+CaHdznS3Ig6YYEZLmH H1mtYHkmiULRFS+3zuKn79OHg+OcKvLwihu2FAVMI9D/28vAGHBcdFtg0fZs8DTCFF eAGYQUtI47QW+yGAHq0lXhwrbj0FJZAA9EbZh1OYmbfcB0giXI/NG0JyYP+MqhL0dp 25Y29wbqWeNyF/qf2ecRuYuvdsB1J0NTYKcl3Oo55gqurozPVky3Y3fXR1AyaTf/vd F+V0T+fdyFJBw== Message-ID: <202033a0-ea65-44de-8119-689e0df0b78e@kernel.org> Date: Fri, 2 Oct 2026 09:48:14 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 40/40] mm/vma: introduce and use vma[_flags]_can_gup() To: "Lorenzo Stoakes (ARM)" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Greg Kroah-Hartman , Dennis Dalessandro , Jason Gunthorpe , Leon Romanovsky , Paul Moore , Stephen Smalley , Jaroslav Kysela , Takashi Iwai , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Doug Gilbert , "James E.J. Bottomley" , "Martin K. Petersen" , Jaya Kumar , Simona Vetter , Helge Deller , Sebastian Reichel , John Hubbard , Peter Xu , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Rik van Riel , Harry Yoo , Juri Lelli , Vincent Guittot , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Arnd Bergmann , Muchun Song , Oscar Salvador , "Matthew Wilcox (Oracle)" , Jan Kara , Marc Zyngier , Oliver Upton , Catalin Marinas , Madhavan Srinivasan , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , "David S. Miller" , Andreas Larsson , Alexander Viro , Christian Brauner , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , Johannes Weiner , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chengming Zhou , Michal Hocko , Miklos Szeredi , Xu Xin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-usb@vger.kernel.org, linux-rdma@vger.kernel.org, selinux@vger.kernel.org, linux-sound@vger.kernel.org, bpf@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev References: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-0-4583d8a23bca@kernel.org> <20260917-b4-mmap-prepare-vma-flag-sanify-v3-40-4583d8a23bca@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: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-40-4583d8a23bca@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/17/26 18:22, Lorenzo Stoakes (ARM) wrote: > GUP cannot be used for VMAs which set VMA_IO_BIT - because memory-mapped > I/O must not be accessed on the user's behalf - or VMA_PFNMAP_BIT - because > PFN maps have no folios which the kernel is permitted to access. The interesting thing will be: what if we want to allow gup for COW'ed pages in PFNMAP. We discussed that already, and it might be a bit harder to squeeze into the new vma[_flags]_can_gup() checks that are also used elsewhere now. Because GUP itself mostly already handles the VMA_PFNMAP_BIT, just has to be taught about vm_normal_page() etc *properly* on all levels. I even have that on my todo list. Updating vma[_flags]_can_gup() won't be enough in that case (ignore VMA_PFNMAP_BIT in cow-mappings), because suddenly we would unlock other code paths that now depend on this helper. Also, there is the secretmem thing I comment on below. I think this also belongs in this helper but other unrelated users don't really want it. Which makes me wonder whether vma[_flags]_can_gup() is actually the right abstraction to use in some other cases that you convert below. For the actual GUP users I think it's the right thing to do. But not for things that are somewhat related to GUP (but actually different) I think you much rather want a separate helper. Long story short: I wonder whether vma[_flags]_can_gup() is the right abstraction, especially for users that don't actually *use* gup but just want slightly similar semantics (no VM_IO|VM_PFNMAP). > > Rather than keeping these checks open-coded, abstract them to > vma_flags_can_gup() and its VMA wrapper vma_can_gup(). > > A number of other places make the same check to decide whether a mapping > can be populated or accessed as GUP would, so update those too. > > While here, drop a reference to 'special' and replace a use of the > deprecated VMA flags API in vma_dump_size(). > > No functional change intended. > > Signed-off-by: Lorenzo Stoakes (ARM) > --- > fs/coredump.c | 4 ++-- > include/linux/mm.h | 29 +++++++++++++++++++++++++++++ > mm/gup.c | 7 +++---- > mm/hmm.c | 3 +-- > mm/memory.c | 14 ++++++++------ > mm/mempolicy.c | 3 ++- > 6 files changed, 45 insertions(+), 15 deletions(-) > > diff --git a/fs/coredump.c b/fs/coredump.c > index fb21fb6703dd..9f729c594c47 100644 > --- a/fs/coredump.c > +++ b/fs/coredump.c > @@ -1616,8 +1616,8 @@ static unsigned long vma_dump_size(struct vm_area_struct *vma, > return 0; > } > > - /* Do not dump I/O mapped devices or special mappings */ > - if (vma->vm_flags & VM_IO) > + /* Do not dump memory-mapped I/O, which may have side effects on read. */ > + if (vma_test(vma, VMA_IO_BIT)) > return 0; > In the end, we use GUP to lookup the pages through get_dump_page(). I think we should just use the gup helper instead? > /* By default, dump shared memory if mapped from an anonymous file. */ > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 5860a3b4dba9..1249e04d7b98 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1777,6 +1777,35 @@ static inline bool vma_is_persistent(const struct vm_area_struct *vma) > return vma_flags_is_persistent(&vma->flags); > } > > +/** > + * vma_flags_can_gup() - Do the specified VMA flags permit GUP to access the > + * mapping's pages? > + * @flags: The VMA flags to test. > + * > + * GUP cannot obtain pages from a PFN map (VMA_PFNMAP_BIT), which may have no > + * struct pages behind it, and must not provide access to memory-mapped I/O > + * (VMA_IO_BIT). > + * > + * Returns: true if GUP may access pages from the mapping, otherwise false. > + */ > +static inline bool vma_flags_can_gup(const vma_flags_t *flags) > +{ > + return !vma_flags_test_any(flags, VMA_IO_BIT, VMA_PFNMAP_BIT); > +} This only covers some things though. See check_vma_flags(): vma_is_secretmem() is another case we universally reject and that is just simply incompatible. In the future, it be an address space flag which we can have from the VMA. So we'd want a vma_can_gup() helper but not necessarily a vma_flags_can_gup() helper. I think this belongs into the vma_can_gup() helper. Also, we should better clarify in the doc that other GUP flags will decide whether GUP is actually allowed. the semantics are a bit vague right now "Do the specified VMA flags permit GUP to access". [...] > diff --git a/mm/hmm.c b/mm/hmm.c > index 2f1e98c6b644..e9569b82a1f0 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -595,8 +595,7 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end, > struct hmm_range *range = hmm_vma_walk->range; > struct vm_area_struct *vma = walk->vma; > > - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)) && > - vma->vm_flags & VM_READ) > + if (vma_can_gup(vma) && vma_test(vma, VMA_READ_BIT)) > return 0; Where do we end up using gup? I don't think we do, because hmm essentially implements an alternative to KVM-style GUP-fast usage. So likely this wants a different helper. > > /* > diff --git a/mm/memory.c b/mm/memory.c > index 6c011979401a..338fce99e711 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2417,11 +2417,11 @@ static bool vm_mixed_zeropage_allowed(struct vm_area_struct *vma) > * be problematic as soon as the zeropage gets replaced by a different > * page due to vma->vm_ops->pfn_mkwrite, because what's mapped would > * now differ to what GUP looked up. FSDAX is incompatible to > - * FOLL_LONGTERM and VM_IO is incompatible to GUP completely (see > - * check_vma_flags). > + * FOLL_LONGTERM and memory-mapped I/O is incompatible to GUP completely > + * (see vma_can_gup()). > */ > return vma->vm_ops && vma->vm_ops->pfn_mkwrite && > - (vma_is_fsdax(vma) || vma->vm_flags & VM_IO); > + (vma_is_fsdax(vma) || vma_test(vma, VMA_IO_BIT)); This looks a bit misplaces in this patch. Also, not spelled out in the patch description? [...] > retry: > pgdp = pgd_offset(mm, address); > @@ -7316,8 +7317,9 @@ static int __access_remote_vm(struct mm_struct *mm, unsigned long addr, > } > > /* > - * Check if this is a VM_IO | VM_PFNMAP VMA, which > - * we can access using slightly different code. > + * GUP failed, perhaps because this is a mapping it > + * cannot handle (see vma_can_gup()) - such mappings may > + * provide access via vm_ops->access() instead. > */ > bytes = 0; > #ifdef CONFIG_HAVE_IOREMAP_PROT > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 044ffb4f4128..2fd759e348ca 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -2013,7 +2013,8 @@ SYSCALL_DEFINE5(get_mempolicy, int __user *, policy, > > bool vma_migratable(struct vm_area_struct *vma) > { > - if (vma->vm_flags & (VM_IO | VM_PFNMAP)) > + /* Pages which GUP cannot obtain cannot be migrated either. */ > + if (!vma_can_gup(vma)) > return false; It's slightly confusing, because we don't really use GUP (except in one scenario for lookup_node). -- Cheers, David