Re: [RESEND PATCH v1] mm/vmalloc: fix page mapping if vm_area_alloc_pages() with high order fallback to order 0

[Uladzislau Rezki <urezki@gmail.com>]

On Thu, Aug 08, 2024 at 08:19:56PM +0800, Hailong Liu wrote:
> The __vmap_pages_range_noflush() assumes its argument pages** contains
> pages with the same page shift. However, since commit e9c3cda4d86e
> ("mm, vmalloc: fix high order __GFP_NOFAIL allocations"), if gfp_flags
> includes __GFP_NOFAIL with high order in vm_area_alloc_pages()
> and page allocation failed for high order, the pages** may contain
> two different page shifts (high order and order-0). This could
> lead __vmap_pages_range_noflush() to perform incorrect mappings,
> potentially resulting in memory corruption.
> 
> Users might encounter this as follows (vmap_allow_huge = true, 2M is for PMD_SIZE):
> kvmalloc(2M, __GFP_NOFAIL|GFP_X)
>     __vmalloc_node_range_noprof(vm_flags=VM_ALLOW_HUGE_VMAP)
>         vm_area_alloc_pages(order=9) ---> order-9 allocation failed and fallback to order-0
>             vmap_pages_range()
>                 vmap_pages_range_noflush()
>                     __vmap_pages_range_noflush(page_shift = 21) ----> wrong mapping happens
> 
> We can remove the fallback code because if a high-order
> allocation fails, __vmalloc_node_range_noprof() will retry with
> order-0. Therefore, it is unnecessary to fallback to order-0
> here. Therefore, fix this by removing the fallback code.
> 
> Fixes: e9c3cda4d86e ("mm, vmalloc: fix high order __GFP_NOFAIL allocations")
> Signed-off-by: Hailong Liu <hailong.liu@oppo.com>
> Reported-by: Tangquan Zheng <zhengtangquan@oppo.com>
> Cc: <stable@vger.kernel.org>
> CC: Barry Song <21cnbao@gmail.com>
> CC: Baoquan He <bhe@redhat.com>
> CC: Matthew Wilcox <willy@infradead.org>
> ---
>  mm/vmalloc.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 6b783baf12a1..af2de36549d6 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3584,15 +3584,8 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  			page = alloc_pages_noprof(alloc_gfp, order);
>  		else
>  			page = alloc_pages_node_noprof(nid, alloc_gfp, order);
> -		if (unlikely(!page)) {
> -			if (!nofail)
> -				break;
> -
> -			/* fall back to the zero order allocations */
> -			alloc_gfp |= __GFP_NOFAIL;
> -			order = 0;
> -			continue;
> -		}
> +		if (unlikely(!page))
> +			break;
> 
>  		/*
>  		 * Higher order allocations must be able to be treated as
> ---
> Sorry for fat fingers. with .rej file. resend this.
> 
> Baoquan suggests set page_shift to 0 if fallback in (2 and concern about
> performance of retry with order-0. But IMO with retry,
> - Save memory usage if high order allocation failed.
> - Keep consistancy with align and page-shift.
> - make use of bulk allocator with order-0
> 
> [2] https://lore.kernel.org/lkml/20240725035318.471-1-hailong.liu@oppo.com/
> --
> 2.30.0
>
Makes sense to me.

Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

Thank you!

--
Uladzislau Rezki