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

[Oleksandr Tyshchenko <olekstysh@gmail.com>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

Take page offset into the account when calculating the number of pages
to be granted.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.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);
 	grant_ref_t grant;
 	dma_addr_t dma_handle;
 
@@ -185,7 +185,8 @@ static void xen_grant_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
 				     unsigned long attrs)
 {
 	struct xen_grant_dma_data *data;
-	unsigned int i, n_pages = PFN_UP(size);
+	unsigned long offset = dma_handle & (PAGE_SIZE - 1);
+	unsigned int i, n_pages = PFN_UP(offset + size);
 	grant_ref_t grant;
 
 	if (WARN_ON(dir == DMA_NONE))
-- 
2.25.1