[PATCH v14 3/5] mm/vmalloc: use physical page count in vread_iter() for VM_ALLOC areas

[Shivam Kalra via B4 Relay]

From: Shivam Kalra <shivamkalra98@xxxxxxxxxxx>

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().

Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Shivam Kalra <shivamkalra98@xxxxxxxxxxx>
---
 mm/vmalloc.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 3e159b74cfab..2f606cfade9b 100644
--- 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 << PAGE_SHIFT) :
+				       get_vm_area_size(vm);
+		else
+			size = va_size(va);
 
 		if (addr >= vaddr + size)
 			goto next_va;

-- 
2.43.0