linux-kernel - Re: [PATCH 1/1] device-dax: Correct pgoff align in dax_set

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Message-Id: <20240927104646.3a0b777b5114ec62becd7f47@linux-foundation.org>
Date: Fri, 27 Sep 2024 10:46:46 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Kun(llfl)" <llfl@...ux.alibaba.com>
Cc: linux-kernel@...r.kernel.org, Dan Williams <dan.j.williams@...el.com>,
 Joao Martins <joao.m.martins@...cle.com>
Subject: Re: [PATCH 1/1] device-dax: Correct pgoff align in
 dax_set_mapping()

(cc's added)

On Fri, 27 Sep 2024 15:45:09 +0800 "Kun(llfl)" <llfl@...ux.alibaba.com> wrote:

> pgoff should be aligned using ALIGN_DOWN() instead of ALIGN(). Otherwise,
> vmf->address not aligned to fault_size will be aligned to the next
> alignment, that can result in memory failure getting the wrong address.
> 
> Fixes: b9b5777f09be ("device-dax: use ALIGN() for determining pgoff")

That's quite an old change.  Can you suggest why it took this long to
be discovered?  What is your userspace doing to trigger this?

> Signed-off-by: Kun(llfl) <llfl@...ux.alibaba.com>
> Tested-by: JianXiong Zhao <zhaojianxiong.zjx@...baba-inc.com>
> ---
>  drivers/dax/device.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index 9c1a729cd77e..6d74e62bbee0 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -86,7 +86,7 @@ static void dax_set_mapping(struct vm_fault *vmf, pfn_t pfn,
>  		nr_pages = 1;
>  
>  	pgoff = linear_page_index(vmf->vma,
> -			ALIGN(vmf->address, fault_size));
> +			ALIGN_DOWN(vmf->address, fault_size));
>  
>  	for (i = 0; i < nr_pages; i++) {
>  		struct page *page = pfn_to_page(pfn_t_to_pfn(pfn) + i);
> -- 
> 2.43.0