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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:
Hello Xenia, Juergen
[sorry for the possible format issues]
>
> On 10/5/22 20:48, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>>
>> Take page offset into the account when calculating the number of pages
>> to be granted.
>>
>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>> 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.
+1
I think this will need another patch for switching grant-dma-ops.c to
use XEN_PAGE_SIZE and XEN_PAGE_SHIFT.
+1
I can create a separate patch for converting on top of this series, it would be nice to clarify one point.
So I will convert PAGE_SIZE/PAGE_SHIFT to XEN_PAGE_SIZE/XEN_PAGE_SHIFT respectively (where appropriate).
Should the PFN_UP be converted to XEN_PFN_UP *or* use gnttab_count_grant() explicitly? Personally I would prefer the former, but would also be ok with the latter.
Juergen
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