mm/vmalloc: use physical page count in vread_iter() for VM_ALLOC areas

For VM_ALLOC areas in vread_iter(), derive the vm area size from
vm->nr_pages rather than get_vm_area_size().

Only VM_ALLOC areas are subject to vrealloc() shrinking, which frees pages
without reducing the virtual reservation size.  Switch to using
vm->nr_pages for VM_ALLOC areas so the reader remains correct once shrink
support is added.  Other mapping types (vmap, ioremap) do not initialize
nr_pages and will continue using get_vm_area_size().

[shivamkalra98@zohomail.in: add an nr_pages check]
Link: https://lore.kernel.org/aff47da5-4fd5-481d-be18-e1eb99639490@zohomail.in
Link: https://lore.kernel.org/20260519-vmalloc-shrink-v14-3-70b96ee3e9c9@zohomail.in
Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 3e159b74cfab18901f2f0377cb9fb18d1f3040c6..bc21bf8e188bbbaab8bfc05ccc6ff70e9e1ecf20 100644 (file)
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4666,7 +4666,18 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
                smp_rmb();
 
                vaddr = (char *) va->va_start;
-               size = vm ? get_vm_area_size(vm) : va_size(va);
+               if (vm)
+                       /*
+                        * For VM_ALLOC areas, use nr_pages rather than
+                        * get_vm_area_size() because vrealloc() may shrink
+                        * the mapping without updating area->size. Other
+                        * mapping types (vmap, ioremap) don't set nr_pages.
+                        */
+                       size = (vm->flags & VM_ALLOC && vm->nr_pages) ?
+                                      (vm->nr_pages << PAGE_SHIFT) :
+                                      get_vm_area_size(vm);
+               else
+                       size = va_size(va);
 
                if (addr >= vaddr + size)
                        goto next_va;