vfio: Set MemoryRegionOps:max_access_size and min_access_size

Sets valid.max_access_size and valid.min_access_size to ensure safe
8-byte accesses to vfio. Today, 8-byte accesses are broken into pairs
of 4-byte calls that goes unprotected:

qemu_mutex_lock locked mutex 0x10905ad8
  vfio_region_write  (0001:03:00.0:region1+0xc0, 0x2020c, 4)
qemu_mutex_unlock unlocked mutex 0x10905ad8
qemu_mutex_lock locked mutex 0x10905ad8
  vfio_region_write  (0001:03:00.0:region1+0xc4, 0xa0000, 4)
qemu_mutex_unlock unlocked mutex 0x10905ad8

which occasionally leads to:

qemu_mutex_lock locked mutex 0x10905ad8
  vfio_region_write  (0001:03:00.0:region1+0xc0, 0x2030c, 4)
qemu_mutex_unlock unlocked mutex 0x10905ad8
qemu_mutex_lock locked mutex 0x10905ad8
  vfio_region_write  (0001:03:00.0:region1+0xc0, 0x1000c, 4)
qemu_mutex_unlock unlocked mutex 0x10905ad8
qemu_mutex_lock locked mutex 0x10905ad8
  vfio_region_write  (0001:03:00.0:region1+0xc4, 0xb0000, 4)
qemu_mutex_unlock unlocked mutex 0x10905ad8
qemu_mutex_lock locked mutex 0x10905ad8
  vfio_region_write  (0001:03:00.0:region1+0xc4, 0xa0000, 4)
qemu_mutex_unlock unlocked mutex 0x10905ad8

causing strange errors in guest OS. With this patch, such accesses
are protected by the same lock guard:

qemu_mutex_lock locked mutex 0x10905ad8
vfio_region_write  (0001:03:00.0:region1+0xc0, 0x2000c, 4)
vfio_region_write  (0001:03:00.0:region1+0xc4, 0xb0000, 4)
qemu_mutex_unlock unlocked mutex 0x10905ad8

This happens because the 8-byte write should be broken into 4-byte
writes by memory.c:access_with_adjusted_size() in order to be under
the same lock. Today, it's done in exec.c:address_space_write_continue()
which was able to handle only 4 bytes due to a zero'ed
valid.max_access_size (see exec.c:memory_access_size()).

Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index 6b33b9f..6572c07 100644 (file)
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -190,6 +190,10 @@ const MemoryRegionOps vfio_region_ops = {
     .read = vfio_region_read,
     .write = vfio_region_write,
     .endianness = DEVICE_LITTLE_ENDIAN,
+    .valid = {
+        .min_access_size = 1,
+        .max_access_size = 8,
+    },
 };
 
 /*