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 9908649481E; Mon, 12 Oct 2026 15:03:38 +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=1791817420; cv=none; b=tQBQ+7ZVGq9YUzQl31A+ITW4LH/xdNPZ+WPP5rVNTc4WwCvXwaewvirEqJ4pDoaLiCIhOkX3BWj3vDEadyfvUZPodI6pHqHNW1NiyH8GebShCppjUEofQO2Cy/zCD9mtd8sj67jH01D/6s7Z+RaGdjr+DQXUBL0PurqzB147xIE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791817420; c=relaxed/simple; bh=aHQw7jLC9yoNpf42E094akGseItqG9rcuu4btcy5hHk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rj/8BDut0S/Octh+FG4rsO6AmBiOe5zkLjZp7KvLIs6ly3ETOLBdO8LRBfyGfzNXRt/vJpYCDSjPDtQub20FNC2ljSNRqHXtQyWFjDQesc36kNIjaFlHpuhxNEkWScXzZmxh3hQiVp6TRX9+fztd6KWiWb68sUg0gTaEOmDYCKo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KqQnzUmK; 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="KqQnzUmK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AE88D1F0089B; Mon, 12 Oct 2026 15:03:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791817418; bh=TUxOJIoEwWGSOtnlIj5KDXixurt7xGhOIGc9/JpBlPw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=KqQnzUmKbn/q8oL6O0MmGCPP5O+Y6m2jAfrhciRJULIkfNkMEFSgUq3BTPaW+lXQx GIwV4tZup+P4INDs4Gn6nMeTOyRttCGB24ku/aRmE4h4WcBzlEyPvcWIHvQsluvDPe ljJQY7vjnwKB4kDQMjmJr95y6KkjQ1QY4GJ0jzz1aEiI5jrcTnKctyGRt+DiJUzcVl 47GeIw3nxp9Q1Ghh3zHPmCdVZscbz0DjbAe1gvPifzTBpsYgdm/5vuHzgvbF8sqMDn r1xUZgUlhap/cdcEC7S+qkylXJ9w9p9Qhm4cMonxJ4hpaAzFFcuPOeDysNEgt9wr+t bj7khxv0wkoSQ== Message-ID: <56cc2787-134b-48f0-a9e2-840f57b28607@kernel.org> Date: Mon, 12 Oct 2026 17:03:02 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 07/38] mm: add mmap action for discontiguous kernel page mapping 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. 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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, Ihor Solodrai , Bert Karwatzki References: <20261009-b4-mmap-prepare-vma-flag-sanify-v5-0-923b70125b1e@kernel.org> <20261009-b4-mmap-prepare-vma-flag-sanify-v5-7-923b70125b1e@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: <20261009-b4-mmap-prepare-vma-flag-sanify-v5-7-923b70125b1e@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/9/26 20:04, Lorenzo Stoakes (ARM) wrote: > The existing kernel page mapping mmap actions allow for partial and full > mapping of an array of struct page pointers. > > However some drivers require the mapping of discontiguous ranges. Permit > this by providing discontig_kernel_page_ops which allows a driver to > specify how the operation should begin and how batches of pages should be > retrieved. > > It uses the minimum exposed interface to do so, providing address, page > offset and both vm_private_data state and a local private state object. > > ops->init can establish state for the operation, and ops->get outputs the > pages to map and their count. Should an error arise the core unmaps the > VMA, invoking vm_ops->close, which is therefore where any state established > by ops->init is released. > > Also update the compatibility layer to do this too via > compat_mmap_action_abort(). > > Batches may not exceed the VMA, but may map less than its full range in > case the driver wishes to allow the user to map an area larger than the > available data. > > To use it, users invoke mmap_action_map_discontig_kernel_pages() with > initial local private state and a set of operations. > > Users can then use one of the provided helper functions to perform an > action: > > * discontig_kernel_map_abort() - Abort and leave the mapping as it has > been accumulated so far. > * discontig_kernel_map_page() - Map a single page, or a compound page given > its head page. > * discontig_kernel_map_page_range() - Maps a struct page ** array of a > specified count, mapping only those pages which fit in the VMA. > > While here, update vm_insert_page() and vm_insert_pages() to assert the > mmap write lock is held rather than the bizarre assert !mmap_read_trylock() > and use the new VMA API so all code paths are consistent. > > Also convert a BUG_ON() to a VM_WARN_ON_ONCE() in vm_insert_page(). > > The userland VMA tests are updated accordingly. > > Acked-by: Zi Yan > Signed-off-by: Lorenzo Stoakes (ARM) Finally finding time to go over this. In the future I want to have more time to review such massive series, as it causes severe stress to be forced to review this last minute before it goes upstream. So if I push back in order to give me some more room to breathe in the future it's nothing personal, I just have to keep my sanity somehow. I hate being forced to review because we pick up stuff way to early. There is just way too much other stuff going on. I'm planning on picking up most stuff I maintain in the next cycle. For cross-component stuff (esp. VMA) I expect Andrew to pick stuff up until we tackle this once cycle later. > +static inline > +void mmap_action_map_discontig_kernel_pages(struct vm_area_desc *desc, > + void *init_private, const struct discontig_kernel_page_ops *ops) > +{ > + struct mmap_action *action = &desc->action; > + > + action->type = MMAP_DISCONTIG_KERNEL_PAGES; > + action->map_kernel_discontig.init_private = init_private; > + action->map_kernel_discontig.ops = ops; > +} > + > int mmap_action_prepare(struct vm_area_desc *desc); > int mmap_action_complete(struct vm_area_struct *vma, > struct mmap_action *action, bool is_compat); There is a mixture of two tab vs. different in your changes. > > +static inline void > +discontig_kernel_map_abort(struct discontig_kernel_page_state *state) > +{ > + state->action = DISCONTIG_KERNEL_PAGE_ABORT; > +} > + > +static inline void > +discontig_kernel_map_page(struct discontig_kernel_page_state *state, > + struct page *page) > +{ > + struct folio *folio = page_folio(page); > + > + if (folio_test_large(folio)) { > + VM_WARN_ON_ONCE(page != folio_page(folio, 0)); > + state->action = DISCONTIG_KERNEL_PAGE_MAP_COMPOUND_PAGE; > + state->__folio = folio; > + state->__nr_pages = min(state->nr_pages_remain, > + folio_nr_pages(folio)); > + } else { > + state->action = DISCONTIG_KERNEL_PAGE_MAP_PAGE; > + state->__page = page; > + state->__nr_pages = 1; > + } Why are both separate? Isn't it sufficient to represent that through _page + _nr_pages > 1 ? See below. > +} > + > +static inline void > +discontig_kernel_map_page_range(struct discontig_kernel_page_state *state, > + struct page **page_arr, unsigned long nr_pages) Is this actually "map_pages"? A range is rather a number of consectuive pages part of the same folio/compound page, no? (we call insert_pages() later ... ) > +{ > + state->action = DISCONTIG_KERNEL_PAGE_MAP_PAGE_RANGE; > + state->__page_arr = page_arr; > + state->__nr_pages = min(nr_pages, state->nr_pages_remain); So we expect all of them to be non-compound? [...] > diff --git a/mm/internal.h b/mm/internal.h > index fc4e249e2343..557e629db8c5 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -1515,6 +1515,9 @@ int simple_ioremap_prepare(struct vm_area_desc *desc); > int map_kernel_pages_prepare(struct vm_area_desc *desc); > int map_kernel_pages_complete(struct vm_area_struct *vma, > struct mmap_action *action); > +int map_discontig_kernel_pages_prepare(struct vm_area_desc *desc); > +int map_discontig_kernel_pages_complete(struct vm_area_struct *vma, > + struct mmap_action *action); > > static inline int io_remap_pfn_range_prepare(struct vm_area_desc *desc) > { > diff --git a/mm/memory.c b/mm/memory.c > index 448342883e9d..e5c1d1c35bc7 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2599,27 +2599,34 @@ int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr, > > if (!range_in_vma(vma, addr, end)) > return -EFAULT; > - if (!(vma->vm_flags & VM_MIXEDMAP)) { > - VM_WARN_ON_ONCE(mmap_read_trylock(vma->vm_mm)); > - VM_WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP); > - vm_flags_set(vma, VM_MIXEDMAP); > + if (!vma_test(vma, VMA_MIXEDMAP_BIT)) { > + mmap_assert_write_locked(vma->vm_mm); > + VM_WARN_ON_ONCE(vma_test(vma, VMA_PFNMAP_BIT)); I would prefer to have these changes in a separate patch. Or is it strictly required to have this in this very patch? > + vma_start_write(vma); > + vma_set_flags(vma, VMA_MIXEDMAP_BIT); > } > /* Defer page refcount checking till we're about to map that page. */ > return insert_pages(vma, addr, pages, num, vma->vm_page_prot); > } > EXPORT_SYMBOL(vm_insert_pages); > > +static void __map_kernel_pages_prepare(struct vm_area_desc *desc) > +{ > + if (vma_desc_test(desc, VMA_MIXEDMAP_BIT)) > + return; > + > + mmap_assert_write_locked(desc->mm); > + VM_WARN_ON_ONCE(vma_desc_test(desc, VMA_PFNMAP_BIT)); > + vma_desc_set_flags(desc, VMA_MIXEDMAP_BIT); > +} > + > int map_kernel_pages_prepare(struct vm_area_desc *desc) > { > const struct mmap_action *action = &desc->action; > const unsigned long addr = action->map_kernel.start; > unsigned long nr_pages, end; > > - if (!vma_desc_test(desc, VMA_MIXEDMAP_BIT)) { > - VM_WARN_ON_ONCE(mmap_read_trylock(desc->mm)); > - VM_WARN_ON_ONCE(vma_desc_test(desc, VMA_PFNMAP_BIT)); > - vma_desc_set_flags(desc, VMA_MIXEDMAP_BIT); > - } > + __map_kernel_pages_prepare(desc); > > nr_pages = action->map_kernel.nr_pages; > end = addr + PAGE_SIZE * nr_pages; > @@ -2640,6 +2647,98 @@ int map_kernel_pages_complete(struct vm_area_struct *vma, > &nr_pages, vma->vm_page_prot); > } > > +int map_discontig_kernel_pages_prepare(struct vm_area_desc *desc) > +{ > + const struct mmap_action *action = &desc->action; > + const struct discontig_kernel_page_ops *ops = > + action->map_kernel_discontig.ops; > + > + /* At minimum need to be able to get pages. */ > + if (WARN_ON_ONCE(!ops || !ops->get)) > + return -EINVAL; > + > + __map_kernel_pages_prepare(desc); > + return 0; > +} > + > +static int apply_discontig_action(struct vm_area_struct *vma, > + struct discontig_kernel_page_state *state) > +{ > + unsigned long nr_pages = state->__nr_pages; > + unsigned long addr = state->addr; > + unsigned long i; > + > + if (state->action == DISCONTIG_KERNEL_PAGE_MAP_PAGE) > + return insert_page(vma, addr, state->__page, > + vma->vm_page_prot, /*mkwrite=*/false); > + if (state->action == DISCONTIG_KERNEL_PAGE_MAP_PAGE_RANGE) > + return insert_pages(vma, addr, state->__page_arr, > + &nr_pages, vma->vm_page_prot); > + > + /* Compound folio - have to iterate through each page. */ > + for (i = 0; i < nr_pages; i++, addr += PAGE_SIZE) { > + struct page *page = folio_page(state->__folio, i); > + int err; > + > + err = insert_page(vma, addr, page, vma->vm_page_prot, > + /*mkwrite=*/false); > + if (err) > + return err; > + } Summarizing some of my comments below, I wonder if this could be: DISCONTIG_KERNEL_PAGE_MAP_PAGES - array of individual apges DISCONTIG_KERNEL_PAGE_MAP_CONTIG_PAGES - 1..N contiguous pages if (state->action == DISCONTIG_KERNEL_PAGE_MAP_PAGES) return insert_pages(vma, addr, state->__page_arr, &nr_pages, vma->vm_page_prot); VM_WARN_ON_ONCE(state->action != DISCONTIG_KERNEL_PAGE_MAP_CONTIG_PAGES) for (i = 0; i < nr_pages; i++, addr += PAGE_SIZE) { struct page *page = state->__page + i; int err; err = insert_page(vma, addr, page, vma->vm_page_prot, /*mkwrite=*/false); if (err) return err; } ... -- Cheers, David