xenpaging: handle evict failures

Evict of a nominated gfn must fail if some other process mapped the
page without checking the p2mt of that gfn first.
Add a check to cancel eviction if the page usage count is not 1.

Handle the possible eviction failure in the page-in paths.
After nominate and before evict, something may check the p2mt and call
populate. Handle this case and let the gfn enter the page-in path. The
gfn may still be connected to a mfn, so there is no need to allocate a
new page in prep.

Adjust do_mmu_update to return -ENOENT only if the gfn has entered the
page-in path and if it is not yet connected to a mfn. Otherwise
linux_privcmd_map_foreign_bulk() may loop forever.

Add MEM_EVENT_FLAG_EVICT_FAIL to inform pager that a page-in request for
a possible not-evicted page was sent. xenpaging does currently not need
that flag because failure to evict a gfn will be caught.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/tools/xenpaging/xenpaging.c b/tools/xenpaging/xenpaging.c
index 1ab756efb2..7fbb177c70 100644
--- a/tools/xenpaging/xenpaging.c
+++ b/tools/xenpaging/xenpaging.c
@@ -734,10 +734,12 @@ int main(int argc, char *argv[])
             }
             else
             {
-                DPRINTF("page already populated (domain = %d; vcpu = %d;"
-                        " gfn = %"PRIx64"; paused = %d)\n",
-                        paging->mem_event.domain_id, req.vcpu_id,
-                        req.gfn, req.flags & MEM_EVENT_FLAG_VCPU_PAUSED);
+                DPRINTF("page %s populated (domain = %d; vcpu = %d;"
+                        " gfn = %"PRIx64"; paused = %d; evict_fail = %d)\n",
+                        req.flags & MEM_EVENT_FLAG_EVICT_FAIL ? "not" : "already",
+                        paging->mem_event.domain_id, req.vcpu_id, req.gfn,
+                        !!(req.flags & MEM_EVENT_FLAG_VCPU_PAUSED) ,
+                        !!(req.flags & MEM_EVENT_FLAG_EVICT_FAIL) );
 
                 /* Tell Xen to resume the vcpu */
                 /* XXX: Maybe just check if the vcpu was paused? */