linux-kernel - Re: [PATCH] xen/virtio: Convert PAGE_SIZE/PAGE_SHIFT/PFN

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Message-ID: <8c65d2dc-9901-5863-62a4-054f6fb7c1f3@suse.com>
Date:   Fri, 7 Oct 2022 06:46:29 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Oleksandr Tyshchenko <Oleksandr_Tyshchenko@...m.com>,
        Xenia Ragiadakou <burzalodowa@...il.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <olekstysh@...il.com>
Subject: Re: [PATCH] xen/virtio: Convert PAGE_SIZE/PAGE_SHIFT/PFN_UP to Xen
 counterparts

On 06.10.22 23:13, Oleksandr Tyshchenko wrote:
> 
> On 06.10.22 20:59, Xenia Ragiadakou wrote:
> 
> Hello Xenia
> 
>>
>> On 10/6/22 15:09, Oleksandr Tyshchenko wrote:
>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
>>>
>>> Although XEN_PAGE_SIZE is equal to PAGE_SIZE (4KB) for now, it would
>>> be more correct to use Xen specific #define-s as XEN_PAGE_SIZE can
>>> be changed at some point in the future.
>>>
>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>

...

>> So, the calculated number of grants may differ.
> 
> Good point, I think you are right, so we need to additionally use
> xen_offset_in_page() macro in xen_grant_dma_map_page(),
> 
> something like that to be squashed with current patch:
> 
> 
> diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> index 9d5eca6d638a..bb984dc05deb 100644
> --- a/drivers/xen/grant-dma-ops.c
> +++ b/drivers/xen/grant-dma-ops.c
> @@ -169,7 +169,7 @@ 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 = XEN_PFN_UP(offset + size);
> +       unsigned int i, n_pages = XEN_PFN_UP(xen_offset_in_page(offset)
> + size);

I'd rather introduce another local variable "xen_offset", as it is used
twice.



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