[PATCH v3 0/3] xen/swiotlb: fix an issue and improve swiotlb-xen

[PATCH v3 0/3] xen/swiotlb: fix an issue and improve swiotlb-xen

[Juergen Gross]

While hunting an issue in swiotlb-xen I stumbled over a wrong test
and found some areas for improvement.

Juergen Gross (3):
  xen/swiotlb: fix condition for calling xen_destroy_contiguous_region()
  xen/swiotlb: simplify range_straddles_page_boundary()
  xen/swiotlb: remember having called xen_create_contiguous_region()

 drivers/xen/swiotlb-xen.c  | 34 ++++++++++------------------------
 include/linux/page-flags.h |  4 ++++
 2 files changed, 14 insertions(+), 24 deletions(-)

-- 
2.16.4

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[PATCH v3 1/3] xen/swiotlb: fix condition for calling xen_destroy_contiguous_region()

[Juergen Gross]

The condition in xen_swiotlb_free_coherent() for deciding whether to
call xen_destroy_contiguous_region() is wrong: in case the region to
be freed is not contiguous calling xen_destroy_contiguous_region() is
the wrong thing to do: it would result in inconsistent mappings of
multiple PFNs to the same MFN. This will lead to various strange
crashes or data corruption.

Instead of calling xen_destroy_contiguous_region() in that case a
warning should be issued as that situation should never occur.

Cc: stable@vger.kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
V2: always issue a warning in case xen_destroy_contiguous_region()
    isn't called (Jan Beulich)
---
 drivers/xen/swiotlb-xen.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index d53f3493a6b9..50fd7de54969 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -361,8 +361,8 @@ 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)) ||
-	    range_straddles_page_boundary(phys, size))
+	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
+		     range_straddles_page_boundary(phys, size)))
 		xen_destroy_contiguous_region(phys, order);
 
 	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
-- 
2.16.4

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[PATCH v3 2/3] xen/swiotlb: simplify range_straddles_page_boundary()

[Juergen Gross]

range_straddles_page_boundary() is open coding several macros from
include/xen/page.h. Use those instead. Additionally there is no need
to have check_pages_physically_contiguous() as a separate function as
it is used only once, so merge it into range_straddles_page_boundary().

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 drivers/xen/swiotlb-xen.c | 28 ++++++----------------------
 1 file changed, 6 insertions(+), 22 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 50fd7de54969..37ddcfcfbb21 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -83,34 +83,18 @@ static inline dma_addr_t xen_virt_to_bus(void *address)
 	return xen_phys_to_bus(virt_to_phys(address));
 }
 
-static int check_pages_physically_contiguous(unsigned long xen_pfn,
-					     unsigned int offset,
-					     size_t length)
+static inline int range_straddles_page_boundary(phys_addr_t p, size_t size)
 {
-	unsigned long next_bfn;
-	int i;
-	int nr_pages;
+	unsigned long next_bfn, xen_pfn = XEN_PFN_DOWN(p);
+	unsigned int i, nr_pages = XEN_PFN_UP(xen_offset_in_page(p) + size);
 
 	next_bfn = pfn_to_bfn(xen_pfn);
-	nr_pages = (offset + length + XEN_PAGE_SIZE-1) >> XEN_PAGE_SHIFT;
 
-	for (i = 1; i < nr_pages; i++) {
+	for (i = 1; i < nr_pages; i++)
 		if (pfn_to_bfn(++xen_pfn) != ++next_bfn)
-			return 0;
-	}
-	return 1;
-}
+			return 1;
 
-static inline int range_straddles_page_boundary(phys_addr_t p, size_t size)
-{
-	unsigned long xen_pfn = XEN_PFN_DOWN(p);
-	unsigned int offset = p & ~XEN_PAGE_MASK;
-
-	if (offset + size <= XEN_PAGE_SIZE)
-		return 0;
-	if (check_pages_physically_contiguous(xen_pfn, offset, size))
-		return 0;
-	return 1;
+	return 0;
 }
 
 static int is_xen_swiotlb_buffer(dma_addr_t dma_addr)
-- 
2.16.4

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[PATCH v3 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@suse.com>
---
V2: add PG_xen_remapped alias for PG_owner_priv_1 (Boris Ostrovsky)
    only clear page flag in case of sane conditions (Jan Beulich)
V3: use TestClearPageXenRemapped() (Jan Beulich)
---
 drivers/xen/swiotlb-xen.c  | 4 +++-
 include/linux/page-flags.h | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 37ddcfcfbb21..ceb681cf64bb 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -322,6 +322,7 @@ 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;
@@ -346,7 +347,8 @@ 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)) &&
+	    TestClearPageXenRemapped(virt_to_page(vaddr)))
 		xen_destroy_contiguous_region(phys, order);
 
 	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..fc503a47e7db 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 +331,8 @@ 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)
+	TESTCLEARFLAG(XenRemapped, xen_remapped, PF_NO_COMPOUND)
 
 PAGEFLAG(Reserved, reserved, PF_NO_COMPOUND)
 	__CLEARPAGEFLAG(Reserved, reserved, PF_NO_COMPOUND)
-- 
2.16.4

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