virtio-iommu: Fix 64kB host page size VFIO device assignment

When running on a 64kB page size host and protecting a VFIO device
with the virtio-iommu, qemu crashes with this kind of message:

qemu-kvm: virtio-iommu page mask 0xfffffffffffff000 is incompatible
with mask 0x20010000
qemu: hardware error: vfio: DMA mapping failed, unable to continue

This is due to the fact the IOMMU MR corresponding to the VFIO device
is enabled very late on domain attach, after the machine init.
The device reports a minimal 64kB page size but it is too late to be
applied. virtio_iommu_set_page_size_mask() fails and this causes
vfio_listener_region_add() to end up with hw_error();

To work around this issue, we transiently enable the IOMMU MR on
machine init to collect the page size requirements and then restore
the bypass state.

Fixes: 90519b9 ("virtio-iommu: Add bypass mode support to assigned device")
Signed-off-by: Eric Auger <eric.auger@redhat.com>

Message-Id: <20230705165118.28194-2-eric.auger@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Tested-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>

hw/virtio/trace-events

@@ -133,6 +133,7 @@ virtio_iommu_set_page_size_mask(const char *name, uint64_t old, uint64_t new) "m
 virtio_iommu_notify_flag_add(const char *name) "add notifier to mr %s"
 virtio_iommu_notify_flag_del(const char *name) "del notifier from mr %s"
 virtio_iommu_switch_address_space(uint8_t bus, uint8_t slot, uint8_t fn, bool on) "Device %02x:%02x.%x switching address space (iommu enabled=%d)"
+virtio_iommu_freeze_granule(uint64_t page_size_mask) "granule set to 0x%"PRIx64
 
 # virtio-mem.c
 virtio_mem_send_response(uint16_t type) "type=%" PRIu16

hw/virtio/virtio-iommu.c

@@ -25,6 +25,7 @@
 #include "hw/virtio/virtio.h"
 #include "sysemu/kvm.h"
 #include "sysemu/reset.h"
+#include "sysemu/sysemu.h"
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "trace.h"
@@ -1106,12 +1107,12 @@ static int virtio_iommu_set_page_size_mask(IOMMUMemoryRegion *mr,
     }
 
     /*
-     * After the machine is finalized, we can't change the mask anymore. If by
+     * Once the granule is frozen we can't change the mask anymore. If by
      * chance the hotplugged device supports the same granule, we can still
      * accept it. Having a different masks is possible but the guest will use
      * sub-optimal block sizes, so warn about it.
      */
-    if (phase_check(PHASE_MACHINE_READY)) {
+    if (s->granule_frozen) {
         int new_granule = ctz64(new_mask);
         int cur_granule = ctz64(cur_mask);
 
@@ -1146,6 +1147,28 @@ static void virtio_iommu_system_reset(void *opaque)
 
 }
 
+static void virtio_iommu_freeze_granule(Notifier *notifier, void *data)
+{
+    VirtIOIOMMU *s = container_of(notifier, VirtIOIOMMU, machine_done);
+    int granule;
+
+    if (likely(s->config.bypass)) {
+        /*
+         * Transient IOMMU MR enable to collect page_size_mask requirements
+         * through memory_region_iommu_set_page_size_mask() called by
+         * VFIO region_add() callback
+         */
+         s->config.bypass = false;
+         virtio_iommu_switch_address_space_all(s);
+         /* restore default */
+         s->config.bypass = true;
+         virtio_iommu_switch_address_space_all(s);
+    }
+    s->granule_frozen = true;
+    granule = ctz64(s->config.page_size_mask);
+    trace_virtio_iommu_freeze_granule(BIT(granule));
+}
+
 static void virtio_iommu_device_realize(DeviceState *dev, Error **errp)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
@@ -1189,6 +1212,9 @@ static void virtio_iommu_device_realize(DeviceState *dev, Error **errp)
         error_setg(errp, "VIRTIO-IOMMU is not attached to any PCI bus!");
     }
 
+    s->machine_done.notify = virtio_iommu_freeze_granule;
+    qemu_add_machine_init_done_notifier(&s->machine_done);
+
     qemu_register_reset(virtio_iommu_system_reset, s);
 }
 
@@ -1198,6 +1224,7 @@ static void virtio_iommu_device_unrealize(DeviceState *dev)
     VirtIOIOMMU *s = VIRTIO_IOMMU(dev);
 
     qemu_unregister_reset(virtio_iommu_system_reset, s);
+    qemu_remove_machine_init_done_notifier(&s->machine_done);
 
     g_hash_table_destroy(s->as_by_busptr);
     if (s->domains) {

include/hw/virtio/virtio-iommu.h

@@ -61,6 +61,8 @@ struct VirtIOIOMMU {
     QemuRecMutex mutex;
     GTree *endpoints;
     bool boot_bypass;
+    Notifier machine_done;
+    bool granule_frozen;
 };
 
 #endif