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

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Date:   Thu, 6 Oct 2022 10:05:22 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Xenia Ragiadakou <burzalodowa@...il.com>,
        Oleksandr Tyshchenko <olekstysh@...il.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH 1/2] xen/virtio: Fix n_pages calculation in
 xen_grant_dma_map(unmap)_page()

On 06.10.22 09:35, Xenia Ragiadakou wrote:
> 
> On 10/5/22 20:48, 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")
>> ---
>>   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);
> 
> Here, why do we use PFN_UP and not XEN_PFN_UP?
> Also, since the variable 'n_pages' seems to refer to the number of grants 
> (unless I got it all entirely wrong ...), wouldn't it be more suitable to call 
> explicitly gnttab_count_grant()?

Good point.

I think this will need another patch for switching grant-dma-ops.c to
use XEN_PAGE_SIZE and XEN_PAGE_SHIFT.


Juergen


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