[RFC PATCH v3 2/5] util/vfio-helpers: Report error on unsupported host architectures

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

The vfio-helpers implementation expects a TYPEv1 IOMMU, see
qemu_vfio_init_pci:

  263     if (!ioctl(s->container, VFIO_CHECK_EXTENSION, VFIO_TYPE1_IOMMU)) {
  264         error_setg_errno(errp, errno, "VFIO IOMMU check failed");

Thus POWER SPAPR IOMMU is obviously not supported.

The implementation only cares about host page size alignment
(usually 4KB on X86), not the IOMMU one, which is be problematic
on Aarch64, when 64MB page size is used. So Aarch64 is not
supported neither.

Report an error when the host architecture is different than X86:

 $ qemu-system-aarch64 \
    -drive file=nvme://0001:01:00.0/1,if=none,id=drive0 \
    -device virtio-blk-pci,drive=drive0
  qemu-system-aarch64: -drive file=nvme://0001:01:00.0/1,if=none,id=drive0: QEMU VFIO utility is not supported on this architecture

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
Cc: Eric Auger <eric.auger@redhat.com>
Cc: Drew Jones <drjones@redhat.com>
Cc: Laurent Vivier <lvivier@redhat.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
---
 util/vfio-helpers.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/util/vfio-helpers.c b/util/vfio-helpers.c
index e399e330e26..60017936e3e 100644
--- a/util/vfio-helpers.c
+++ b/util/vfio-helpers.c
@@ -420,14 +420,38 @@ static void qemu_vfio_open_common(QEMUVFIOState *s)
     qemu_ram_foreach_block(qemu_vfio_init_ramblock, s);
 }
 
+/**
+ * Return if the host architecture is supported.
+ *
+ * aarch64: IOMMU page alignment not respected
+ * ppc64:   SPAPR IOMMU window not configured
+ * x86-64:  Only architecture validated
+ * other:   Untested
+ */
+static bool qemu_vfio_arch_supported(void)
+{
+    bool supported = false;
+
+#if defined(HOST_X86_64)
+    supported = true;
+#endif
+
+    return supported;
+}
 /**
  * Open a PCI device, e.g. "0000:00:01.0".
  */
 QEMUVFIOState *qemu_vfio_open_pci(const char *device, Error **errp)
 {
     int r;
-    QEMUVFIOState *s = g_new0(QEMUVFIOState, 1);
+    QEMUVFIOState *s;
 
+    if (!qemu_vfio_arch_supported()) {
+        error_setg(errp,
+                   "QEMU VFIO utility is not supported on this architecture");
+        return NULL;
+    }
+    s = g_new0(QEMUVFIOState, 1);
     r = qemu_vfio_init_pci(s, device, errp);
     if (r) {
         g_free(s);
-- 
2.26.2