xen/grant: Introduce helpers to split a page into grant

Currently, a grant is always based on the Xen page granularity (i.e
4KB). When Linux is using a different page granularity, a single page
will be split between multiple grants.

The new helpers will be in charge of splitting the Linux page into grants
and call a function given by the caller on each grant.

Also provide an helper to count the number of grants within a given
contiguous region.

Note that the x86/include/asm/xen/page.h is now including
xen/interface/grant_table.h rather than xen/grant_table.h. It's
necessary because xen/grant_table.h depends on asm/xen/page.h and will
break the compilation. Furthermore, only definition in
interface/grant_table.h is required.

Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index b922fa4bb4a1049bc9efa84aaf97b2e2ab391897..fe58e3a935deac5c3cbdc6d0b74302c9387f95fb 100644 (file)
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -12,7 +12,7 @@
 #include <asm/pgtable.h>
 
 #include <xen/interface/xen.h>
-#include <xen/grant_table.h>
+#include <xen/interface/grant_table.h>
 #include <xen/features.h>
 
 /* Xen machine address */

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index a4b702c9ac685c7050d02bc46121c6990ee28191..dbeaa67dec47c987630ecd4fd13562f0403dcbf8 100644 (file)
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -776,6 +776,32 @@ void gnttab_batch_copy(struct gnttab_copy *batch, unsigned count)
 }
 EXPORT_SYMBOL_GPL(gnttab_batch_copy);
 
+void gnttab_foreach_grant_in_range(struct page *page,
+                                  unsigned int offset,
+                                  unsigned int len,
+                                  xen_grant_fn_t fn,
+                                  void *data)
+{
+       unsigned int goffset;
+       unsigned int glen;
+       unsigned long xen_pfn;
+
+       len = min_t(unsigned int, PAGE_SIZE - offset, len);
+       goffset = xen_offset_in_page(offset);
+
+       xen_pfn = page_to_xen_pfn(page) + XEN_PFN_DOWN(offset);
+
+       while (len) {
+               glen = min_t(unsigned int, XEN_PAGE_SIZE - goffset, len);
+               fn(pfn_to_gfn(xen_pfn), goffset, glen, data);
+
+               goffset = 0;
+               xen_pfn++;
+               len -= glen;
+       }
+}
+EXPORT_SYMBOL_GPL(gnttab_foreach_grant_in_range);
+
 int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
                    struct gnttab_map_grant_ref *kmap_ops,
                    struct page **pages, unsigned int count)

diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index 4478f4b4aae2ff06473f2aff0e0100684f11c2bf..05b5b08c2afc90fd767976c334e56213170bd8e1 100644 (file)
--- a/include/xen/grant_table.h
+++ b/include/xen/grant_table.h
@@ -45,8 +45,10 @@
 #include <asm/xen/hypervisor.h>
 
 #include <xen/features.h>
+#include <xen/page.h>
 #include <linux/mm_types.h>
 #include <linux/page-flags.h>
+#include <linux/kernel.h>
 
 #define GNTTAB_RESERVED_XENSTORE 1
 
@@ -224,4 +226,44 @@ static inline struct xen_page_foreign *xen_page_foreign(struct page *page)
 #endif
 }
 
+/* Split Linux page in chunk of the size of the grant and call fn
+ *
+ * Parameters of fn:
+ *     gfn: guest frame number
+ *     offset: offset in the grant
+ *     len: length of the data in the grant.
+ *     data: internal information
+ */
+typedef void (*xen_grant_fn_t)(unsigned long gfn, unsigned int offset,
+                              unsigned int len, void *data);
+
+void gnttab_foreach_grant_in_range(struct page *page,
+                                  unsigned int offset,
+                                  unsigned int len,
+                                  xen_grant_fn_t fn,
+                                  void *data);
+
+/* Helper to get to call fn only on the first "grant chunk" */
+static inline void gnttab_for_one_grant(struct page *page, unsigned int offset,
+                                       unsigned len, xen_grant_fn_t fn,
+                                       void *data)
+{
+       /* The first request is limited to the size of one grant */
+       len = min_t(unsigned int, XEN_PAGE_SIZE - (offset & ~XEN_PAGE_MASK),
+                   len);
+
+       gnttab_foreach_grant_in_range(page, offset, len, fn, data);
+}
+
+/* Get the number of grant in a specified region
+ *
+ * start: Offset from the beginning of the first page
+ * len: total length of data (can cross multiple page)
+ */
+static inline unsigned int gnttab_count_grant(unsigned int start,
+                                             unsigned int len)
+{
+       return XEN_PFN_UP(xen_offset_in_page(start) + len);
+}
+
 #endif /* __ASM_GNTTAB_H__ */