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 <[email protected]> --- include/hw/virtio/virtio-iommu.h | 1 + hw/virtio/virtio-iommu.c | 23 +++++++++++++++++++++-- 2 files changed, 22 insertions(+), 2 deletions(-) diff --git a/include/hw/virtio/virtio-iommu.h b/include/hw/virtio/virtio-iommu.h index 273e35c04bc..4c66989ca4e 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 c2883a2f6c8..cd08dc39eca 100644 --- a/hw/virtio/virtio-iommu.c +++ b/hw/virtio/virtio-iommu.c @@ -689,6 +689,25 @@ static void virtio_iommu_report_fault(VirtIOIOMMU *viommu, uint8_t reason, } +static bool virtio_iommu_bypass_is_allowed(VirtIOIOMMU *s) +{ + VirtIODevice *vdev = &s->parent_obj; + + /* + * Allow bypass if: + * - boot_bypass is enabled and the BYPASS feature hasn't yet been + * acknowledged. + * - the BYPASS feature has been negotiated. + */ + if (s->boot_bypass && !(vdev->status & VIRTIO_CONFIG_S_FEATURES_OK)) { + return true; + } + if (virtio_vdev_has_feature(vdev, VIRTIO_IOMMU_F_BYPASS)) { + return true; + } + return false; +} + static IOMMUTLBEntry virtio_iommu_translate(IOMMUMemoryRegion *mr, hwaddr addr, IOMMUAccessFlags flag, int iommu_idx) @@ -715,8 +734,7 @@ 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 = virtio_iommu_bypass_is_allowed(s); sid = virtio_iommu_get_bdf(sdev); @@ -1156,6 +1174,7 @@ 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(), }; -- 2.30.0
