[Xen-devel] [PATCH 3/3] xen-netback: handle page straddling in xenvif_set_hash_mapping()

["Jan Beulich" <JBeulich@xxxxxxxx>]

There's no guarantee that the mapping array doesn't cross a page
boundary. Use a second grant copy operation if necessary.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

---
 drivers/net/xen-netback/hash.c |   25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

--- 4.19-rc1-xen-netback-set-hash-mapping.orig/drivers/net/xen-netback/hash.c
+++ 4.19-rc1-xen-netback-set-hash-mapping/drivers/net/xen-netback/hash.c
@@ -334,28 +334,39 @@ u32 xenvif_set_hash_mapping(struct xenvi
                            u32 off)
 {
        u32 *mapping = vif->hash.mapping[!vif->hash.mapping_sel];
-       struct gnttab_copy copy_op = {
+       unsigned int nr = 1;
+       struct gnttab_copy copy_op[2] = {{
                .source.u.ref = gref,
                .source.domid = vif->domid,
                .dest.domid = DOMID_SELF,
                .len = len * sizeof(*mapping),
                .flags = GNTCOPY_source_gref
-       };
+       }};
 
        if ((off + len < off) || (off + len > vif->hash.size) ||
            len > XEN_PAGE_SIZE / sizeof(*mapping))
                return XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER;
 
-       copy_op.dest.u.gmfn = virt_to_gfn(mapping + off);
-       copy_op.dest.offset = xen_offset_in_page(mapping + off);
+       copy_op[0].dest.u.gmfn = virt_to_gfn(mapping + off);
+       copy_op[0].dest.offset = xen_offset_in_page(mapping + off);
+       if (copy_op[0].dest.offset + copy_op[0].len > XEN_PAGE_SIZE) {
+               copy_op[1] = copy_op[0];
+               copy_op[1].source.offset = XEN_PAGE_SIZE - 
copy_op[0].dest.offset;
+               copy_op[1].dest.u.gmfn = virt_to_gfn(mapping + off + len);
+               copy_op[1].dest.offset = 0;
+               copy_op[1].len = copy_op[0].len - copy_op[1].source.offset;
+               copy_op[0].len = copy_op[1].source.offset;
+               nr = 2;
+       }
 
        memcpy(mapping, vif->hash.mapping[vif->hash.mapping_sel],
               vif->hash.size * sizeof(*mapping));
 
-       if (copy_op.len != 0) {
-               gnttab_batch_copy(&copy_op, 1);
+       if (copy_op[0].len != 0) {
+               gnttab_batch_copy(copy_op, nr);
 
-               if (copy_op.status != GNTST_okay)
+               if (copy_op[0].status != GNTST_okay ||
+                   copy_op[nr - 1].status != GNTST_okay)
                        return XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER;
        }
 





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