Re: [PATCH v12 3/5] mm/vmalloc: use physical page count in vread_iter()

[Uladzislau Rezki <urezki@gmail.com>]

On Tue, Apr 28, 2026 at 01:54:18AM +0530, Shivam Kalra via B4 Relay wrote:
> From: Shivam Kalra <shivamkalra98@zohomail.in>
> 
> Update vread_iter() to derive the vm area size from vm->nr_pages rather
> than get_vm_area_size().
> 
> Currently both values are equivalent, but the upcoming vrealloc() shrink
> functionality will free pages without reducing the virtual reservation
> size. After such a shrink, the old get_vm_area_size() based calculation
> would overestimate the mapped range, causing vread_iter() to attempt
> reading from unmapped addresses. Switch to vm->nr_pages now so the
> reader remains correct once shrink support is added.
> 
> Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>
> ---
>  mm/vmalloc.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 9cb3e287a1e8..65e0a23efb3b 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -4661,7 +4661,14 @@ 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)
> +			/*
> +			 * Cannot use get_vm_area_size() because realloc()
> +			 * may shrink the mapping and area->size may be outdated.
> +			 */
> +			size = vm->nr_pages << PAGE_SHIFT;
> +		else
> +			size = va_size(va);
>  
>  		if (addr >= vaddr + size)
>  			goto next_va;
> 
> -- 
> 2.43.0
> 
> 
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

--
Uladzislau Rezki