linux-kernel - Re: [PATCH 1/2] xen/virtio: Fix n_pages calculation in xen_grant_dma_map(unmap)

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Message-ID: <alpine.DEB.2.22.394.2210051707380.3690179@ubuntu-linux-20-04-desktop>
Date:   Wed, 5 Oct 2022 17:07:53 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Oleksandr Tyshchenko <olekstysh@...il.com>
cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH 1/2] xen/virtio: Fix n_pages calculation in
 xen_grant_dma_map(unmap)_page()

On Wed, 5 Oct 2022, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
> 
> Take page offset into the account when calculating the number of pages
> to be granted.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
> Fixes: d6aca3504c7d ("xen/grant-dma-ops: Add option to restrict memory access under Xen")

Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>


> ---
>  drivers/xen/grant-dma-ops.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> index 8973fc1e9ccc..1998d0e8ce82 100644
> --- a/drivers/xen/grant-dma-ops.c
> +++ b/drivers/xen/grant-dma-ops.c
> @@ -153,7 +153,7 @@ static dma_addr_t xen_grant_dma_map_page(struct device *dev, struct page *page,
>  					 unsigned long attrs)
>  {
>  	struct xen_grant_dma_data *data;
> -	unsigned int i, n_pages = PFN_UP(size);
> +	unsigned int i, n_pages = PFN_UP(offset + size);
>  	grant_ref_t grant;
>  	dma_addr_t dma_handle;
>  
> @@ -185,7 +185,8 @@ static void xen_grant_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
>  				     unsigned long attrs)
>  {
>  	struct xen_grant_dma_data *data;
> -	unsigned int i, n_pages = PFN_UP(size);
> +	unsigned long offset = dma_handle & (PAGE_SIZE - 1);
> +	unsigned int i, n_pages = PFN_UP(offset + size);
>  	grant_ref_t grant;
>  
>  	if (WARN_ON(dir == DMA_NONE))
> -- 
> 2.25.1
>