vfio: Start improving VFIO/EEH interface

At present the code handling IBM's Enhanced Error Handling (EEH) interface
on VFIO devices operates by bypassing the usual VFIO logic with
vfio_container_ioctl().  That's a poorly designed interface with unclear
semantics about exactly what can be operated on.

In particular it operates on a single vfio container internally (hence the
name), but takes an address space and group id, from which it deduces the
container in a rather roundabout way.  groupids are something that code
outside vfio shouldn't even be aware of.

This patch creates new interfaces for EEH operations.  Internally we
have vfio_eeh_container_op() which takes a VFIOContainer object
directly.  For external use we have vfio_eeh_as_ok() which determines
if an AddressSpace is usable for EEH (at present this means it has a
single container with exactly one group attached), and vfio_eeh_as_op()
which will perform an operation on an AddressSpace in the unambiguous case,
and otherwise returns an error.

This interface still isn't great, but it's enough of an improvement to
allow a number of cleanups in other places.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Acked-by: Alex Williamson <alex.williamson@redhat.com>

hw/vfio/common.c

@@ -1137,3 +1137,98 @@ int vfio_container_ioctl(AddressSpace *as, int32_t groupid,
 
     return vfio_container_do_ioctl(as, groupid, req, param);
 }
+
+/*
+ * Interfaces for IBM EEH (Enhanced Error Handling)
+ */
+static bool vfio_eeh_container_ok(VFIOContainer *container)
+{
+    /*
+     * As of 2016-03-04 (linux-4.5) the host kernel EEH/VFIO
+     * implementation is broken if there are multiple groups in a
+     * container.  The hardware works in units of Partitionable
+     * Endpoints (== IOMMU groups) and the EEH operations naively
+     * iterate across all groups in the container, without any logic
+     * to make sure the groups have their state synchronized.  For
+     * certain operations (ENABLE) that might be ok, until an error
+     * occurs, but for others (GET_STATE) it's clearly broken.
+     */
+
+    /*
+     * XXX Once fixed kernels exist, test for them here
+     */
+
+    if (QLIST_EMPTY(&container->group_list)) {
+        return false;
+    }
+
+    if (QLIST_NEXT(QLIST_FIRST(&container->group_list), container_next)) {
+        return false;
+    }
+
+    return true;
+}
+
+static int vfio_eeh_container_op(VFIOContainer *container, uint32_t op)
+{
+    struct vfio_eeh_pe_op pe_op = {
+        .argsz = sizeof(pe_op),
+        .op = op,
+    };
+    int ret;
+
+    if (!vfio_eeh_container_ok(container)) {
+        error_report("vfio/eeh: EEH_PE_OP 0x%x: "
+                     "kernel requires a container with exactly one group", op);
+        return -EPERM;
+    }
+
+    ret = ioctl(container->fd, VFIO_EEH_PE_OP, &pe_op);
+    if (ret < 0) {
+        error_report("vfio/eeh: EEH_PE_OP 0x%x failed: %m", op);
+        return -errno;
+    }
+
+    return 0;
+}
+
+static VFIOContainer *vfio_eeh_as_container(AddressSpace *as)
+{
+    VFIOAddressSpace *space = vfio_get_address_space(as);
+    VFIOContainer *container = NULL;
+
+    if (QLIST_EMPTY(&space->containers)) {
+        /* No containers to act on */
+        goto out;
+    }
+
+    container = QLIST_FIRST(&space->containers);
+
+    if (QLIST_NEXT(container, next)) {
+        /* We don't yet have logic to synchronize EEH state across
+         * multiple containers */
+        container = NULL;
+        goto out;
+    }
+
+out:
+    vfio_put_address_space(space);
+    return container;
+}
+
+bool vfio_eeh_as_ok(AddressSpace *as)
+{
+    VFIOContainer *container = vfio_eeh_as_container(as);
+
+    return (container != NULL) && vfio_eeh_container_ok(container);
+}
+
+int vfio_eeh_as_op(AddressSpace *as, uint32_t op)
+{
+    VFIOContainer *container = vfio_eeh_as_container(as);
+
+    if (!container) {
+        return -ENODEV;
+    }
+    return vfio_eeh_container_op(container, op);
+}

include/hw/vfio/vfio.h

@@ -5,5 +5,7 @@
 
 extern int vfio_container_ioctl(AddressSpace *as, int32_t groupid,
                                 int req, void *param);
+bool vfio_eeh_as_ok(AddressSpace *as);
+int vfio_eeh_as_op(AddressSpace *as, uint32_t op);
 
 #endif