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linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev, Ihor Solodrai , Bert Karwatzki Subject: Re: [PATCH v5 07/38] mm: add mmap action for discontiguous kernel page mapping Message-ID: 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> <56cc2787-134b-48f0-a9e2-840f57b28607@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56cc2787-134b-48f0-a9e2-840f57b28607@kernel.org> X-Stat-Signature: sgfpsktjjc1jtrs8iyzbeg3jswfdcpym X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D92E840006 X-HE-Tag: 1791827221-149346 X-HE-Meta: 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 rGf/3T6F lg6bDBcnQq/kNoiO0k4j6bJq4o02Yrl9ViV7YjBM3wGKXI8C5fgaVHDbk03T8SHjvCMhY0VNTdsw+apMyvkq/2mItLT/nKrujFVITqP14C8FrQEOR55Y4y+NXQq0GovJ66r4MGmpYiZHibW88G5vrrE19Km7uyFdBhoF8/Y9/8e76svcdfeIYsVC98e/66N9KYCpUQ0ooWmK6wbCDCwXvr0YMgRJjBCM31ReNb4tIqKUia3LVHvwHWGaGWce3ADpsl/YHHAIhga5dU92M6ihdd1gS13cfn7ktacqmor29tnDC196+L9xWlohZzdvvCCTXhKhaYaFbxnB8jJQA42YV7M4B7tjNBr0E= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Oct 12, 2026 at 05:03:02PM +0200, David Hildenbrand (Arm) wrote: > 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. OK I understand, sorry for sending such a large series. I already delayed it from last cycle and sent early in rc2, but I understand there's been a lot of volume in this one. I've been working evenings and weekends myself to keep up with review (and failing), so I get how thankless it can be (LPC was also unhelpfully timed!) I will try to split things out more in future, this had a lot of dependencies so it wasn't clear that made sense + wouldn't just cause more stress over a longer period otherwise. > > > > +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. OK. mm is fairly inconsistent about this, I will convert all to 2 tabs. > > > > > +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. Ack yup that works. > > > +} > > + > > +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 ... ) Sure, can change. > > > +{ > > + 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? Yup this matches existing insert_pages() behaviour. > > > [...] > > > 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? That was because Suren raised the 'assert on mmap_read_trylock()' thing and I wanted to get the other cases here to be consistent. I will split it out into another 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 OK. > > > 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; > } > ... OK. Will respin for v6. > > -- > Cheers, > > David -- Cheers, Lorenzo