[PATCH 2/3] virtio-iommu: Default to bypass during boot

[Jean-Philippe Brucker]

Currently the virtio-iommu device must be programmed before it allows
DMA from any PCI device. This can make the VM entirely unusable when a
virtio-iommu driver isn't present, for example in a bootloader that
loads the OS from storage.

Similarly to the other vIOMMU implementations, default to DMA bypassing
the IOMMU during boot. Add a "boot-bypass" option that lets users change
this behavior.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
---
 include/hw/virtio/virtio-iommu.h |  1 +
 hw/virtio/virtio-iommu.c         | 28 +++++++++++++++++++++++-----
 hw/virtio/trace-events           |  4 ++--
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/include/hw/virtio/virtio-iommu.h b/include/hw/virtio/virtio-iommu.h
index 273e35c04b..4c66989ca4 100644
--- a/include/hw/virtio/virtio-iommu.h
+++ b/include/hw/virtio/virtio-iommu.h
@@ -58,6 +58,7 @@ struct VirtIOIOMMU {
     GTree *domains;
     QemuMutex mutex;
     GTree *endpoints;
+    bool boot_bypass;
 };
 
 #endif
diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
index 1b23e8e18c..82edeaa101 100644
--- a/hw/virtio/virtio-iommu.c
+++ b/hw/virtio/virtio-iommu.c
@@ -728,8 +728,7 @@ static IOMMUTLBEntry 
virtio_iommu_translate(IOMMUMemoryRegion *mr, hwaddr addr,
         .perm = IOMMU_NONE,
     };
 
-    bypass_allowed = virtio_vdev_has_feature(&s->parent_obj,
-                                             VIRTIO_IOMMU_F_BYPASS);
+    bypass_allowed = s->config.bypass;
 
     sid = virtio_iommu_get_bdf(sdev);
 
@@ -828,7 +827,8 @@ static void virtio_iommu_get_config(VirtIODevice *vdev, 
uint8_t *config_data)
                                   config->input_range.start,
                                   config->input_range.end,
                                   config->domain_range.end,
-                                  config->probe_size);
+                                  config->probe_size,
+                                  config->bypass);
     memcpy(config_data, &dev->config, sizeof(struct virtio_iommu_config));
 }
 
@@ -836,13 +836,29 @@ static void virtio_iommu_set_config(VirtIODevice *vdev,
                                       const uint8_t *config_data)
 {
     struct virtio_iommu_config config;
+    VirtIOIOMMU *dev = VIRTIO_IOMMU(vdev);
 
     memcpy(&config, config_data, sizeof(struct virtio_iommu_config));
+
+    if (config.bypass != dev->config.bypass) {
+        if (!virtio_vdev_has_feature(vdev, VIRTIO_IOMMU_F_BYPASS_CONFIG)) {
+            virtio_error(vdev, "cannot set config.bypass");
+            return;
+        }
+        if (config.bypass != 0 && config.bypass != 1) {
+            warn_report("invalid config.bypass value '%d'", config.bypass);
+            dev->config.bypass = 0;
+            return;
+        }
+        dev->config.bypass = config.bypass;
+    }
+
     trace_virtio_iommu_set_config(config.page_size_mask,
                                   config.input_range.start,
                                   config.input_range.end,
                                   config.domain_range.end,
-                                  config.probe_size);
+                                  config.probe_size,
+                                  config.bypass);
 }
 
 static uint64_t virtio_iommu_get_features(VirtIODevice *vdev, uint64_t f,
@@ -986,6 +1002,7 @@ static void virtio_iommu_device_realize(DeviceState *dev, 
Error **errp)
     s->config.input_range.end = -1UL;
     s->config.domain_range.end = 32;
     s->config.probe_size = VIOMMU_PROBE_SIZE;
+    s->config.bypass = s->boot_bypass;
 
     virtio_add_feature(&s->features, VIRTIO_RING_F_EVENT_IDX);
     virtio_add_feature(&s->features, VIRTIO_RING_F_INDIRECT_DESC);
@@ -993,9 +1010,9 @@ static void virtio_iommu_device_realize(DeviceState *dev, 
Error **errp)
     virtio_add_feature(&s->features, VIRTIO_IOMMU_F_INPUT_RANGE);
     virtio_add_feature(&s->features, VIRTIO_IOMMU_F_DOMAIN_RANGE);
     virtio_add_feature(&s->features, VIRTIO_IOMMU_F_MAP_UNMAP);
-    virtio_add_feature(&s->features, VIRTIO_IOMMU_F_BYPASS);
     virtio_add_feature(&s->features, VIRTIO_IOMMU_F_MMIO);
     virtio_add_feature(&s->features, VIRTIO_IOMMU_F_PROBE);
+    virtio_add_feature(&s->features, VIRTIO_IOMMU_F_BYPASS_CONFIG);
 
     qemu_mutex_init(&s->mutex);
 
@@ -1169,6 +1186,7 @@ static const VMStateDescription vmstate_virtio_iommu = {
 
 static Property virtio_iommu_properties[] = {
     DEFINE_PROP_LINK("primary-bus", VirtIOIOMMU, primary_bus, "PCI", PCIBus *),
+    DEFINE_PROP_BOOL("boot-bypass", VirtIOIOMMU, boot_bypass, true),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
index 8ed19e9d0c..6bc3821ba3 100644
--- a/hw/virtio/trace-events
+++ b/hw/virtio/trace-events
@@ -90,8 +90,8 @@ virtio_mmio_setting_irq(int level) "virtio_mmio setting IRQ 
%d"
 virtio_iommu_device_reset(void) "reset!"
 virtio_iommu_get_features(uint64_t features) "device supports 
features=0x%"PRIx64
 virtio_iommu_device_status(uint8_t status) "driver status = %d"
-virtio_iommu_get_config(uint64_t page_size_mask, uint64_t start, uint64_t end, 
uint32_t domain_range, uint32_t probe_size) "page_size_mask=0x%"PRIx64" 
start=0x%"PRIx64" end=0x%"PRIx64" domain_range=%d probe_size=0x%x"
-virtio_iommu_set_config(uint64_t page_size_mask, uint64_t start, uint64_t end, 
uint32_t domain_range, uint32_t probe_size) "page_size_mask=0x%"PRIx64" 
start=0x%"PRIx64" end=0x%"PRIx64" domain_bits=%d probe_size=0x%x"
+virtio_iommu_get_config(uint64_t page_size_mask, uint64_t start, uint64_t end, 
uint32_t domain_range, uint32_t probe_size, uint8_t bypass) 
"page_size_mask=0x%"PRIx64" start=0x%"PRIx64" end=0x%"PRIx64" domain_range=%d 
probe_size=0x%x bypass=0x%x"
+virtio_iommu_set_config(uint64_t page_size_mask, uint64_t start, uint64_t end, 
uint32_t domain_range, uint32_t probe_size, uint8_t bypass) 
"page_size_mask=0x%"PRIx64" start=0x%"PRIx64" end=0x%"PRIx64" domain_bits=%d 
probe_size=0x%x bypass=0x%x"
 virtio_iommu_attach(uint32_t domain_id, uint32_t ep_id) "domain=%d endpoint=%d"
 virtio_iommu_detach(uint32_t domain_id, uint32_t ep_id) "domain=%d endpoint=%d"
 virtio_iommu_map(uint32_t domain_id, uint64_t virt_start, uint64_t virt_end, 
uint64_t phys_start, uint32_t flags) "domain=%d virt_start=0x%"PRIx64" 
virt_end=0x%"PRIx64 " phys_start=0x%"PRIx64" flags=%d"
-- 
2.33.0