[PATCH v2 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>
---
V2: add PG_xen_remapped alias for PG_owner_priv_1 (Boris Ostrovsky)
    only clear page flag in case of sane conditions (Jan Beulich)
---
 drivers/xen/swiotlb-xen.c  | 6 +++++-
 include/linux/page-flags.h | 3 +++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index aba5247b9145..7e2d9d1b6f63 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;
 		}
+		SetPageXenRemapped(virt_to_page(ret));
 	}
 	memset(ret, 0, size);
 	return ret;
@@ -345,8 +346,11 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 	size = 1UL << (order + XEN_PAGE_SHIFT);
 
 	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
-		     range_straddles_page_boundary(phys, size)))
+		     range_straddles_page_boundary(phys, size)) &&
+	    PageXenRemapped(virt_to_page(vaddr))) {
 		xen_destroy_contiguous_region(phys, order);
+		ClearPageXenRemapped(virt_to_page(vaddr));
+	}
 
 	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
 }
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 9f8712a4b1a5..296480e990f2 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -152,6 +152,8 @@ enum pageflags {
 	PG_savepinned = PG_dirty,
 	/* Has a grant mapping of another (foreign) domain's page. */
 	PG_foreign = PG_owner_priv_1,
+	/* Remapped by swiotlb-xen. */
+	PG_xen_remapped = PG_owner_priv_1,
 
 	/* SLOB */
 	PG_slob_free = PG_private,
@@ -329,6 +331,7 @@ PAGEFLAG(Pinned, pinned, PF_NO_COMPOUND)
 	TESTSCFLAG(Pinned, pinned, PF_NO_COMPOUND)
 PAGEFLAG(SavePinned, savepinned, PF_NO_COMPOUND);
 PAGEFLAG(Foreign, foreign, PF_NO_COMPOUND);
+PAGEFLAG(XenRemapped, xen_remapped, PF_NO_COMPOUND);
 
 PAGEFLAG(Reserved, reserved, PF_NO_COMPOUND)
 	__CLEARPAGEFLAG(Reserved, reserved, PF_NO_COMPOUND)
-- 
2.16.4