[Qemu-devel] [PATCH] vhost: skip ROM sections

[Michael S. Tsirkin]

vhost does not support RO protections on memory at the moment - adding
ROMs would mean that e.g. a buggy guest might change them in-memory - a
condition from which guest reset does not recover. Not nice.

We also definitely don't want to try logging writes into ROMs - in
particular guests set very high addresses for ROM BARs so logging these
writes would waste a lot of memory.  With phys address in the 32T range
we would need 1Gbyte sized log - scanning it would take ages, and
allocating such huge amount of log memory was also reported to fail on
powerpc.

Maybe ROMs could be supported with the iotlb variant -
not sure, but there seems to be no good reason for virtio
to try to do DMA from ROM. So let's just skip ROM memory.

Suggested-by: Laurent Vivier <address@hidden>
Signed-off-by: Michael S. Tsirkin <address@hidden>
---
 hw/virtio/vhost.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 9cacf55..94b8c4a 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -612,7 +612,8 @@ static void vhost_set_memory(MemoryListener *listener,
 
 static bool vhost_section(MemoryRegionSection *section)
 {
-    return memory_region_is_ram(section->mr);
+    return memory_region_is_ram(section->mr) &&
+        !memory_region_is_rom(section->mr);
 }
 
 static void vhost_begin(MemoryListener *listener)
-- 
MST