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

From: Juergen Gross
Date: Thu Oct 06 2022 - 04:05:42 EST

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


Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key

Attachment: OpenPGP_signature
Description: OpenPGP digital signature