[PATCH 3/3] xen/swiotlb: remember having called xen_create_contiguous_region()

[Juergen Gross]

Instead of always calling xen_destroy_contiguous_region() in case the
memory is DMA-able for the used device, do so only in case it has been
made DMA-able via xen_create_contiguous_region() before.

This will avoid a lot of xen_destroy_contiguous_region() calls for
64-bit capable devices.

As the memory in question is owned by swiotlb-xen the PG_owner_priv_1
flag of the first allocated page can be used for remembering.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/swiotlb-xen.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 43b6e65ae256..a72f181d8e20 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -321,6 +321,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 			xen_free_coherent_pages(hwdev, size, ret, (dma_addr_t)phys, attrs);
 			return NULL;
 		}
+		SetPageOwnerPriv1(virt_to_page(ret));
 	}
 	memset(ret, 0, size);
 	return ret;
@@ -344,9 +345,11 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 	/* Convert the size to actually allocated. */
 	size = 1UL << (order + XEN_PAGE_SHIFT);
 
-	if ((dev_addr + size - 1 <= dma_mask) &&
-	    !WARN_ON(range_straddles_page_boundary(phys, size)))
-		xen_destroy_contiguous_region(phys, order);
+	if (PageOwnerPriv1(virt_to_page(vaddr))) {
+		if (!WARN_ON(range_straddles_page_boundary(phys, size)))
+			xen_destroy_contiguous_region(phys, order);
+		ClearPageOwnerPriv1(virt_to_page(vaddr));
+	}
 
 	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
 }
-- 
2.16.4