[Xen-devel] Sub page Grant Table mappings

[Mike Belopuhov <mike.belopuhov@xxxxxxxxxxxx>]

Hi,

I'm trying to get grant table sub page mappings working on Xen 4.5.
I know there have been some changes in the trunk regarding moving src/
dst checks closer together, but I can't test this easily atm.  Please
bear with me for a moment.  Or tell me that it might have been broken
previously.

What I'm trying to do is to map in a 2k cluster from the networking
stack (we call it an mbuf cluster, you might call it skb something)
onto the Netfront Rx ring.  2 clusters fit one page.  Therefore for
one frame address which is a (PA >> 12) I might have 2 entries one
after the other, both with sub_page.length = 2048 but one with a
sub_page.page_off = 2048 and the other with a 0 offset.  Both come
with (GTF_permit_access | GTF_sub_page) flags.

When I do that, Xen stops liking me and says:

(XEN) grant_table.c:2162:d0v1 copy dest out of bounds: 0 < 2048 || 90 > 2048
(XEN) grant_table.c:2162:d0v1 copy dest out of bounds: 0 < 2048 || 119 > 2048
(XEN) grant_table.c:2162:d0v2 copy dest out of bounds: 0 < 2048 || 70 > 2048
(XEN) grant_table.c:2162:d0v2 copy dest out of bounds: 0 < 2048 || 119 > 2048
(XEN) grant_table.c:2162:d0v2 copy dest out of bounds: 0 < 2048 || 119 > 2048
...

The relevant code does this:

    if ( dest_is_gref )
    {
        unsigned dest_off, dest_len;
        rc = __acquire_grant_for_copy(dd, op->dest.u.ref,
                                      current->domain->domain_id, 0,
                                      &d_frame, &d_pg, &dest_off, &dest_len, 1);
        if ( rc != GNTST_okay )
            goto error_out;
        have_d_grant = 1;
        if ( op->dest.offset < dest_off ||
             op->len > dest_len )
            PIN_FAIL(error_out, GNTST_general_error,
                     "copy dest out of bounds: %d < %d || %d > %d\n",
                     op->dest.offset, dest_off,
                     op->len, dest_len);
    }

I fail to understand what am I doing wrong in this case.  Any clues
will be greatly appreciated.

4k clusters mapped in as full_page mappings work as expected.

Cheers,
Mike

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