[PATCH] virtio-iommu: Use qemu_real_host_page_mask as default page_size_mask

[Eric Auger <eric.auger@redhat.com>]

We used to set default page_size_mask to qemu_target_page_mask() but
with VFIO assignment it makes more sense to use the actual host page mask
instead.

So from now on qemu_real_host_page_mask() will be used as a default.
To be able to migrate older code, we increase the vmstat version_id
to 3 and if an older incoming v2 stream is detected we set the previous
default value.

The new default is well adapted to configs where host and guest have
the same page size. This allows to fix hotplugging VFIO devices on a
64kB guest and a 64kB host. This test case has been failing before
and even crashing qemu with hw_error("vfio: DMA mapping failed,
unable to continue") in VFIO common). Indeed the hot-attached VFIO
device would call memory_region_iommu_set_page_size_mask with 64kB
mask whereas after the granule was frozen to 4kB on machine init done.
Now this works. However the new default will prevent 4kB guest on
64kB host because the granule will be set to 64kB which would be
larger than the guest page size. In that situation, the virtio-iommu
driver fails the viommu_domain_finalise() with
"granule 0x10000 larger than system page zie 0x1000".

The current limitation of global granule in the virtio-iommu
should be removed and turned into per domain granule. But
until we get this upgraded, this new default is probably
better because I don't think anyone is currently interested in
running a 4kB page size guest with virtio-iommu on a 64kB host.
However supporting 64kB guest on 64kB host with virtio-iommu and
VFIO looks a more important feature.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
---
 hw/virtio/virtio-iommu.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
index 9d463efc52..b77e3644ea 100644
--- a/hw/virtio/virtio-iommu.c
+++ b/hw/virtio/virtio-iommu.c
@@ -1313,7 +1313,7 @@ static void virtio_iommu_device_realize(DeviceState *dev, Error **errp)
      * in vfio realize
      */
     s->config.bypass = s->boot_bypass;
-    s->config.page_size_mask = qemu_target_page_mask();
+    s->config.page_size_mask = qemu_real_host_page_mask();
     s->config.input_range.end = UINT64_MAX;
     s->config.domain_range.end = UINT32_MAX;
     s->config.probe_size = VIOMMU_PROBE_SIZE;
@@ -1491,13 +1491,16 @@ static int iommu_post_load(void *opaque, int version_id)
      * still correct.
      */
     virtio_iommu_switch_address_space_all(s);
+    if (version_id <= 2) {
+        s->config.page_size_mask = qemu_target_page_mask();
+    }
     return 0;
 }
 
 static const VMStateDescription vmstate_virtio_iommu_device = {
     .name = "virtio-iommu-device",
     .minimum_version_id = 2,
-    .version_id = 2,
+    .version_id = 3,
     .post_load = iommu_post_load,
     .fields = (VMStateField[]) {
         VMSTATE_GTREE_DIRECT_KEY_V(domains, VirtIOIOMMU, 2,
-- 
2.27.0