[PATCH] Linux-HVM, qemu, and xen-balloon.ko

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

George Dunlap wrote:

> There seems to be some sort of a bug when qemu interacts with the
> balloon driver.  Stefano is trying to repro it, but I thought I'd
> share it for people to look at.



There is a bug in qemu_map_cache: if address_index == last_address_index
we don't check that there is a valid_mapping for address_offset in the
bucket.
The following patch fixes it.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

---

diff -r 0ea6bd53cfb6 hw/xen_machine_fv.c
--- a/hw/xen_machine_fv.c	Thu Oct 23 10:26:02 2008 +0100
+++ b/hw/xen_machine_fv.c	Mon Dec 15 11:43:52 2008 +0000
@@ -135,10 +135,11 @@
     unsigned long address_index  = phys_addr >> MCACHE_BUCKET_SHIFT;
     unsigned long address_offset = phys_addr & (MCACHE_BUCKET_SIZE-1);
 
-    if (address_index == last_address_index)
+    entry = &mapcache_entry[address_index % nr_buckets];
+
+    if (address_index == last_address_index &&
+        test_bit(address_offset>>XC_PAGE_SHIFT, entry->valid_mapping))
         return last_address_vaddr + address_offset;
-
-    entry = &mapcache_entry[address_index % nr_buckets];
 
     if (entry->vaddr_base == NULL || entry->paddr_index != address_index ||
         !test_bit(address_offset>>XC_PAGE_SHIFT, entry->valid_mapping))