[RFC PATCH v4 3/5] util/vfio-helpers: Report error when IOMMU page size is not supported

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

This driver uses the host page size to align its memory regions,
but this size is not always compatible with the IOMMU. Add a
check if the size matches, and bails out with listing the sizes
the IOMMU supports.

Example on Aarch64:

 $ qemu-system-aarch64 -M virt -drive if=none,id=nvme0,file=nvme://0006:90:00.0/1,format=raw
 qemu-system-aarch64: -drive if=none,id=nvme0,file=nvme://0006:90:00.0/1,format=raw: Unsupported IOMMU page size: 4 KiB
 Available page size:
  64 KiB
  512 MiB

Suggested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 util/vfio-helpers.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/util/vfio-helpers.c b/util/vfio-helpers.c
index 9a83e6084e5..8f4a3d452ed 100644
--- a/util/vfio-helpers.c
+++ b/util/vfio-helpers.c
@@ -11,6 +11,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/cutils.h"
 #include <sys/ioctl.h>
 #include <linux/vfio.h>
 #include "qapi/error.h"
@@ -316,6 +317,25 @@ static int qemu_vfio_init_pci(QEMUVFIOState *s, const char *device,
         ret = -errno;
         goto fail;
     }
+    if (!(iommu_info.flags & VFIO_IOMMU_INFO_PGSIZES)) {
+        error_setg(errp, "Failed to get IOMMU page size info");
+        ret = -errno;
+        goto fail;
+    }
+    if (!extract64(iommu_info.iova_pgsizes,
+                   ctz64(qemu_real_host_page_size), 1)) {
+        g_autofree char *host_page_size = size_to_str(qemu_real_host_page_size);
+        error_setg(errp, "Unsupported IOMMU page size: %s", host_page_size);
+        error_append_hint(errp, "Available page size:\n");
+        for (int i = 0; i < 64; i++) {
+            if (extract64(iommu_info.iova_pgsizes, i, 1)) {
+                g_autofree char *iova_pgsizes = size_to_str(1UL << i);
+                error_append_hint(errp, " %s\n", iova_pgsizes);
+            }
+        }
+        ret = -EINVAL;
+        goto fail;
+    }
 
     s->device = ioctl(s->group, VFIO_GROUP_GET_DEVICE_FD, device);
 
-- 
2.26.2