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Message-ID: <df17af24-632c-6087-43e0-9e4079959437@suse.com>
Date: Thu, 6 Oct 2022 12:24:20 +0200
From: Juergen Gross <jgross@...e.com>
To: Oleksandr Tyshchenko <olekstysh@...il.com>,
Xenia Ragiadakou <burzalodowa@...il.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
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 12:14, Oleksandr Tyshchenko wrote:
>
>
> On Thu, Oct 6, 2022 at 11:05 AM Juergen Gross <jgross@...e.com
> <mailto:jgross@...e.com>> wrote:
>
> 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@...m.com
> <mailto: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
> <mailto: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.
>
>
> +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).
Yes, that would be the idea.
> 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.
I agree XEN_PFN_UP would be better, especially as XEN_PAGE_SIZE/XEN_PAGE_SHIFT
will be used in the same functions.
Juergen
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