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: 90519b9053 ("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>

diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
index 4e39ed8a9595d67e318938bb99365e1fab42b656..7109cf1a3bcec9670fd25f008011b837bbd75e14 100644 (file)
--- a/hw/virtio/trace-events
+++ b/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

diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
index 1bbad23f4a6ee4ef2d4509d5d4a016d46204edbf..8d0c5e3f325e0f77b28db0401211cb80d31ae916 100644 (file)
--- a/hw/virtio/virtio-iommu.c
+++ b/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) {

diff --git a/include/hw/virtio/virtio-iommu.h b/include/hw/virtio/virtio-iommu.h
index 2ad5ee320be90f1ba57a63270114faaaef8998cb..a93fc5383e0ffee52494134fa3ec894c1324010e 100644 (file)
--- a/include/hw/virtio/virtio-iommu.h
+++ b/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