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

[Juergen Gross <jgross@xxxxxxxx>]

On 06.10.22 09:35, Xenia Ragiadakou wrote:
> 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.

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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