xen: define BIOVEC_PHYS_MERGEABLE()

Impact: allow Xen control of bio merging

When running in Xen domain with device access, we need to make sure
the block subsystem doesn't merge requests across pages which aren't
machine physically contiguous.  To do this, we define our own
BIOVEC_PHYS_MERGEABLE.  When CONFIG_XEN isn't enabled, or we're not
running in a Xen domain, this has identical behaviour to the normal
implementation.  When running under Xen, we also make sure the
underlying machine pages are the same or adjacent.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

2 files changed, 14 insertions, 1 deletions

diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index fcaf838f54be..b47f5da674d3 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -1,4 +1,4 @@
-obj-y   += grant-table.o features.o events.o manage.o
+obj-y   += grant-table.o features.o events.o manage.o biomerge.o
 obj-y   += xenbus/
 
 nostackp := $(call cc-option, -fno-stack-protector)
diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c
new file mode 100644
index 000000000000..ba6eda4b5143
--- /dev/null
+++ b/drivers/xen/biomerge.c
@@ -0,0 +1,13 @@
+#include <linux/bio.h>
+#include <linux/io.h>
+#include <xen/page.h>
+
+bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
+                               const struct bio_vec *vec2)
+{
+        unsigned long mfn1 = pfn_to_mfn(page_to_pfn(vec1->bv_page));
+        unsigned long mfn2 = pfn_to_mfn(page_to_pfn(vec2->bv_page));
+
+        return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) &&
+                ((mfn1 == mfn2) || ((mfn1+1) == mfn2));
+}