mm: add mmap action for discontiguous kernel page mapping

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, as 1..N contiguous pages.
* discontig_kernel_map_pages() - Map a struct page ** array of a specified
  count, mapping only those pages which fit in the VMA.

The userland VMA tests are updated accordingly.

Link: https://lore.kernel.org/20261013-b4-mmap-prepare-vma-flag-sanify-v6-8-1aa3c9b139f9@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Doug Gilbert <dgilbert@interlog.com>
Cc: James Bottomley <james.bottomley@hansenpartnership.com>
Cc: Martin K. Petersen <mkp@kernel.org>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Helge Deller <deller@gmx.de>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Anup Patel <anup@brainfault.org>
Cc: Paul Walmsley <pjw@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Youngjun Park <youngjun.park@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Xu Xin <xu.xin@linux.dev>
Cc: Ihor Solodrai <ihor.solodrai@linux.dev>
Cc: Bert Karwatzki <spasswolf@web.de>

2 files changed, 83 insertions, 2 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index d724c7401798..fc0d4c0a0cb6 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4654,10 +4654,53 @@ static inline void mmap_action_map_kernel_pages_full(struct vm_area_desc *desc,
 				     vma_desc_pages(desc));
 }
 
+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);
 
+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);
+	unsigned long nr_pages = 1;
+
+	if (folio_test_large(folio)) {
+		VM_WARN_ON_ONCE(page != folio_page(folio, 0));
+		nr_pages = folio_nr_pages(folio);
+	}
+
+	state->action = DISCONTIG_KERNEL_PAGE_MAP_CONTIG_PAGES;
+	state->__page = page;
+	state->__nr_pages = min(nr_pages, state->nr_pages_remain);
+}
+
+static inline void
+discontig_kernel_map_pages(struct discontig_kernel_page_state *state,
+		struct page **page_arr, unsigned long nr_pages)
+{
+	state->action = DISCONTIG_KERNEL_PAGE_MAP_PAGES;
+	state->__page_arr = page_arr;
+	state->__nr_pages = min(nr_pages, state->nr_pages_remain);
+}
+
 /* Look up the first VMA which exactly match the interval vm_start ... vm_end */
 static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
 				unsigned long vm_start, unsigned long vm_end)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index bd5c8832d1af..0dead656d3e3 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -818,8 +818,42 @@ enum mmap_action_type {
 	MMAP_NOTHING,
 	MMAP_REMAP_PFN,
 	MMAP_IO_REMAP_PFN,
-	MMAP_SIMPLE_IO_REMAP,	/* I/O remap with guardrails. */
-	MMAP_KERNEL_PAGES,	/* Map kernel page range from array. */
+	MMAP_SIMPLE_IO_REMAP,		/* I/O remap with guardrails. */
+	MMAP_KERNEL_PAGES,		/* Map kernel page range from array. */
+	MMAP_DISCONTIG_KERNEL_PAGES,	/* Map kernel discontig page range. */
+};
+
+enum discontig_kernel_page_action {
+	DISCONTIG_KERNEL_PAGE_ABORT,
+	DISCONTIG_KERNEL_PAGE_MAP_PAGES,	/* Array of individual pages. */
+	DISCONTIG_KERNEL_PAGE_MAP_CONTIG_PAGES,	/* 1..N contiguous pages. */
+};
+
+struct discontig_kernel_page_state {
+	/* Map state. */
+	const unsigned long start;	/* Start address of VMA. */
+	const unsigned long end;	/* End address of VMA. */
+	unsigned long addr;		/* The current address to be mapped. */
+	pgoff_t pgoff;			/* The current pgoff to be mapped. */
+	unsigned long nr_pages_mapped;	/* The number of pages mapped. */
+	unsigned long nr_pages_remain;	/* The number of pages remaining. */
+
+	/* User-defined state. */
+	void *vm_private_data;		/* VMA private data. */
+	void *private;			/* Mapping private data. */
+
+	/* Users should not touch these, use discontig_kernel_map_*() helpers. */
+	enum discontig_kernel_page_action action;
+	union {
+		struct page *__page;
+		struct page **__page_arr;
+	};
+	unsigned long __nr_pages;
+};
+
+struct discontig_kernel_page_ops {
+	int (*init)(void *vm_private_data, void **private);
+	int (*get)(struct discontig_kernel_page_state *state);
 };
 
 /*
@@ -844,6 +878,10 @@ struct mmap_action {
 			unsigned long nr_pages;
 			pgoff_t pgoff;
 		} map_kernel;
+		struct {
+			void *init_private;
+			const struct discontig_kernel_page_ops *ops;
+		} map_kernel_discontig;
 	};
 	enum mmap_action_type type;