Hi, all!
I am working on a zero-copy scenario for x86
and for that I am mapping pages from Dom0 to DomU
(yes, I know there are at least security concerns).
Everything is just fine, e.g. I can map grefs from Dom0 in DomU
with gnttab_map_refs, until I try to mmap those pages in DomU
with vm_insert_page and Xen starts to complain:
(XEN) mm.c:989:d1v0 pg_owner 1 l1e_owner 1, but real_pg_owner 0
(XEN) mm.c:1061:d1v0 Error getting mfn 20675a (pfn 1ac8de) from L1 entry
800000020675a027 for l1e_owner=1, pg_owner=1
So, the offending(?) code is at [1] which doesn't allow the mapping
I want. When removed with
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index f35e3116bb25..aeb93be8b529 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -980,6 +980,7 @@ get_page_from_l1e(
* dom0, until pvfb supports granted mappings. At that time this
* minor hack can go away.
*/
+#if 0
if ( (real_pg_owner == NULL) || (pg_owner == l1e_owner) ||
xsm_priv_mapping(XSM_TARGET, pg_owner, real_pg_owner) )
{
@@ -988,6 +989,7 @@ get_page_from_l1e(
real_pg_owner?real_pg_owner->domain_id:-1);
goto could_not_pin;
}
+#endif
pg_owner = real_pg_owner;
}
I can successfully mmap and use pages from Dom0 in DomU.
Can anybody please explain why the use-case I am trying to implement
is treated as error from Xen's POV and what would be the right way to
do so?
Thank you,
Oleksandr
[1]
http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/mm.c;h=96bc28065076cb5c742a00fa0a5ffe07e9cd6e7c;hb=HEAD#l1001
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