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Thu, 30 Jul 2026 06:04:26 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 30 Jul 2026 15:04:24 +0200 To: Artem Lytkin Cc: linux-mm@kvack.org, akpm@linux-foundation.org, urezki@gmail.com, shivamkalra98@zohomail.in, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/vmalloc: make vm_struct.nr_pages an unsigned long Message-ID: References: <20260729175708.7074-1-iprintercanon@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260729175708.7074-1-iprintercanon@gmail.com> On Wed, Jul 29, 2026 at 08:57:08PM +0300, Artem Lytkin wrote: > A vmalloc area can hold more than 2^32 pages, but the page counts > tracking it are 32 bit. That has produced the same truncation bug twice > already, once in vread_iter() and once in the vrealloc() grow-in-place > check, and it keeps the casts that hide it scattered around the file. > > Widen the field and everything that feeds or consumes it, so the byte > counts derived from it are computed in 64 bit arithmetic without a cast > at each site: > > - vm_area_alloc_pages() takes and returns a page count, and the result > is stored into nr_pages, so its parameter, return type and the > nr_allocated and nr_remaining accumulators widen too. The 100 page > cap on a bulk request stays narrow, only its literal becomes 100UL. > > - nr_small_pages in __vmalloc_area_node() is derived from a 64 bit > size and compared against nr_pages, so it widens as well. Before > this the store truncated for a size of 16 TiB or more, which sized > area->pages from the wrapped count while __vmap_pages_range() still > walked the full size. The cast on array_size next to it was already > redundant and goes away with it. > > - new_nr_pages and old_nr_pages in vrealloc_node_align_noprof() widen, > which drops the four casts on them, and the casts added by the two > preceding patches in vrealloc_node_align_noprof() and vread_iter() > are no longer needed either. > > - vm_area_free_pages() takes a page index range. > > Three loop counters that index area->pages were plain int and would have > overflowed at 2^31 pages: in set_area_direct_map(), in vm_reset_perms() > and in the bulk allocation loop, where the index is seeded from > nr_allocated. They become unsigned long. > > Printing needed fixing in two places. vmalloc_dump_obj() used %u, and > vmalloc_info_show() printed the unsigned field with %d, which would have > shown a negative page count for an area of 8 TiB or more. > show_numa_info() used a single unsigned int as both the page index and > the node id, so the page loop gets its own unsigned long counter. > > The page table walkers are not covered here. vmap_pages_pte_range() and > the levels above it carry the page cursor as int *nr, so a mapping is > still capped independently of the counters this patch widens. Widening > that cursor touches the whole walker and is separate work. > > Nothing outside mm/vmalloc.c needs a change to build or to behave as > before. Those users either index the pages array or multiply the count > by PAGE_SIZE, which is unsigned long already. kexec_handover stores the > count into a 32 bit field of its own ABI, which caps that interface > exactly where it did before. > > On x86-64 this leaves sizeof(struct vm_struct) at 72 bytes when > CONFIG_HAVE_ARCH_HUGE_VMALLOC=n, since the existing padding before > phys_addr absorbs the change, and takes it to 80 when the config is > enabled. Both sizes come from the same kmalloc-96 bucket that > __get_vm_area_node() allocates from, so the footprint per area does not > change either way. > > Suggested-by: Andrew Morton > Assisted-by: Claude:claude-fable-5 > Signed-off-by: Artem Lytkin > --- > include/linux/vmalloc.h | 2 +- > mm/vmalloc.c | 62 ++++++++++++++++++++--------------------- > 2 files changed, 31 insertions(+), 33 deletions(-) > > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h > index d87dc7f77f4e8..a39c20c77efcd 100644 > --- a/include/linux/vmalloc.h > +++ b/include/linux/vmalloc.h > @@ -62,7 +62,7 @@ struct vm_struct { > #ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC > unsigned int page_order; > #endif > - unsigned int nr_pages; > + unsigned long nr_pages; > phys_addr_t phys_addr; > const void *caller; > unsigned long requested_size; > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index baf7e396e3fc7..efd5e42c64e2e 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -3338,7 +3338,7 @@ struct vm_struct *remove_vm_area(const void *addr) > static inline void set_area_direct_map(const struct vm_struct *area, > int (*set_direct_map)(struct page *page)) > { > - int i; > + unsigned long i; > > /* HUGE_VMALLOC passes small pages to set_direct_map */ > for (i = 0; i < area->nr_pages; i++) > @@ -3354,7 +3354,7 @@ static void vm_reset_perms(struct vm_struct *area) > unsigned long start = ULONG_MAX, end = 0; > unsigned int page_order = vm_area_page_order(area); > int flush_dmap = 0; > - int i; > + unsigned long i; > > /* > * Find the start and end range of the direct mappings to make sure that > @@ -3427,10 +3427,10 @@ void vfree_atomic(const void *addr) > * Caller is responsible for unmapping (vunmap_range) and KASAN > * poisoning before calling this. > */ > -static void vm_area_free_pages(struct vm_struct *vm, unsigned int start_idx, > - unsigned int end_idx) > +static void vm_area_free_pages(struct vm_struct *vm, unsigned long start_idx, > + unsigned long end_idx) > { > - unsigned int i; > + unsigned long i; > > if (!(vm->flags & VM_MAP_PUT_PAGES)) { > for (i = start_idx; i < end_idx; i++) > @@ -3642,12 +3642,12 @@ static inline gfp_t vmalloc_gfp_adjust(gfp_t flags, const bool large) > return flags; > } > > -static inline unsigned int > +static inline unsigned long > vm_area_alloc_pages(gfp_t gfp, int nid, > - unsigned int order, unsigned int nr_pages, struct page **pages) > + unsigned int order, unsigned long nr_pages, struct page **pages) > { > - unsigned int nr_allocated = 0; > - unsigned int nr_remaining = nr_pages; > + unsigned long nr_allocated = 0; > + unsigned long nr_remaining = nr_pages; > unsigned int max_attempt_order = MAX_PAGE_ORDER; > struct page *page; > int i; > @@ -3695,7 +3695,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid, > if (!order) { > while (nr_allocated < nr_pages) { > unsigned int nr, nr_pages_request; > - int i; > + unsigned long i; > > /* > * A maximum allowed request is hard-coded and is 100 > @@ -3703,7 +3703,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid, > * long preemption off scenario in the bulk-allocator > * so the range is [1:100]. > */ > - nr_pages_request = min(100U, nr_pages - nr_allocated); > + nr_pages_request = min(100UL, nr_pages - nr_allocated); > > /* memory allocation should consider mempolicy, we can't > * wrongly use nearest node when nid == NUMA_NO_NODE, > @@ -3849,12 +3849,12 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, > unsigned long addr = (unsigned long)area->addr; > unsigned long size = get_vm_area_size(area); > unsigned long array_size; > - unsigned int nr_small_pages = size >> PAGE_SHIFT; > + unsigned long nr_small_pages = size >> PAGE_SHIFT; > unsigned int page_order; > unsigned int flags; > int ret; > > - array_size = (unsigned long)nr_small_pages * sizeof(struct page *); > + array_size = nr_small_pages * sizeof(struct page *); > > /* __GFP_NOFAIL and "noblock" flags are mutually exclusive. */ > if (!gfpflags_allow_blocking(gfp_mask)) > @@ -4352,7 +4352,7 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align > } > > if (size <= old_size) { > - unsigned int new_nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT; > + unsigned long new_nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT; > > /* Zero out "freed" memory, potentially for future realloc. */ > if (want_init_on_free() || want_init_on_alloc(flags)) > @@ -4381,7 +4381,7 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align > !(vm->flags & (VM_FLUSH_RESET_PERMS | VM_USERMAP)) && > gfp_has_io_fs(flags)) { > unsigned long addr = (unsigned long)kasan_reset_tag(p); > - unsigned int old_nr_pages = vm->nr_pages; > + unsigned long old_nr_pages = vm->nr_pages; > > /* > * Use the node lock to synchronize with concurrent > @@ -4394,16 +4394,13 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align > spin_unlock(&vn->busy.lock); > > /* Notify kmemleak of the reduced allocation size before unmapping. */ > - kmemleak_free_part( > - (void *)addr + ((unsigned long)new_nr_pages > - << PAGE_SHIFT), > - (unsigned long)(old_nr_pages - new_nr_pages) > - << PAGE_SHIFT); > + kmemleak_free_part((void *)addr + > + (new_nr_pages << PAGE_SHIFT), > + (old_nr_pages - new_nr_pages) > + << PAGE_SHIFT); > > - vunmap_range(addr + ((unsigned long)new_nr_pages > - << PAGE_SHIFT), > - addr + ((unsigned long)old_nr_pages > - << PAGE_SHIFT)); > + vunmap_range(addr + (new_nr_pages << PAGE_SHIFT), > + addr + (old_nr_pages << PAGE_SHIFT)); > > vm_area_free_pages(vm, new_nr_pages, old_nr_pages); > } > @@ -4415,7 +4412,7 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align > /* > * We already have the bytes available in the allocation; use them. > */ > - if (size <= (unsigned long)vm->nr_pages << PAGE_SHIFT) { > + if (size <= vm->nr_pages << PAGE_SHIFT) { > /* > * No need to zero memory here, as unused memory will have > * already been zeroed at initial allocation time or during > @@ -4722,7 +4719,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count) > * mapping types (vmap, ioremap) don't set nr_pages. > */ > size = (vm->flags & VM_ALLOC && vm->nr_pages) ? > - ((unsigned long)vm->nr_pages << PAGE_SHIFT) : > + (vm->nr_pages << PAGE_SHIFT) : > get_vm_area_size(vm); > else > size = va_size(va); > @@ -5228,7 +5225,7 @@ bool vmalloc_dump_obj(void *object) > struct vmap_area *va; > struct vmap_node *vn; > unsigned long addr; > - unsigned int nr_pages; > + unsigned long nr_pages; > > addr = PAGE_ALIGN((unsigned long) object); > vn = addr_to_node(addr); > @@ -5248,7 +5245,7 @@ bool vmalloc_dump_obj(void *object) > nr_pages = vm->nr_pages; > spin_unlock(&vn->busy.lock); > > - pr_cont(" %u-page vmalloc region starting at %#lx allocated at %pS\n", > + pr_cont(" %lu-page vmalloc region starting at %#lx allocated at %pS\n", > nr_pages, addr, caller); > > return true; > @@ -5266,16 +5263,17 @@ bool vmalloc_dump_obj(void *object) > static void show_numa_info(struct seq_file *m, struct vm_struct *v, > unsigned int *counters) > { > - unsigned int nr; > unsigned int step = 1U << vm_area_page_order(v); > + unsigned long i; > + unsigned int nr; > > if (!counters) > return; > > memset(counters, 0, nr_node_ids * sizeof(unsigned int)); > > - for (nr = 0; nr < v->nr_pages; nr += step) > - counters[page_to_nid(v->pages[nr])] += step; > + for (i = 0; i < v->nr_pages; i += step) > + counters[page_to_nid(v->pages[i])] += step; > for_each_node_state(nr, N_HIGH_MEMORY) > if (counters[nr]) > seq_printf(m, " N%u=%u", nr, counters[nr]); > @@ -5333,7 +5331,7 @@ static int vmalloc_info_show(struct seq_file *m, void *p) > seq_printf(m, " %pS", v->caller); > > if (v->nr_pages) > - seq_printf(m, " pages=%d", v->nr_pages); > + seq_printf(m, " pages=%lu", v->nr_pages); > > if (v->phys_addr) > seq_printf(m, " phys=%pa", &v->phys_addr); > > base-commit: 248951ddc14de84de3910f9b13f51491a8cd91df > prerequisite-patch-id: bc462c518eb9ddcaccad5e1f5fed7cc24512b117 > prerequisite-patch-id: 891688c2e93c570d1c9c7802b46aaba974002684 > -- > 2.43.0 > Makes sense to me. The commit message could be shorter describing just an issue. I was lost when i read it first time. Also: Artem Lytkin (3): mm/vmalloc: fix 32-bit truncation of the area size in vread_iter() mm/vmalloc: fix 32-bit truncation in the vrealloc() grow-in-place check mm/vmalloc: make vm_struct.nr_pages an unsigned long first two fix overlaps. The latest also do it by converting nr_pages to unsigned long and removes (unsigned long) casting introduced by 1 and 2. Maybe just use one commit which is last in this series? Anyway for this Reviewed-by: Uladzislau Rezki (Sony) -- Uladzislau Rezki