hw/i386/acpi-build: Add DMAR support to bypass iommu

hw/i386/acpi-build: Add DMAR support to bypass iommu

In DMAR table, the drhd is set to cover all PCI devices when intel_iommu
is on. To support bypass iommu feature, we need to walk the PCI bus with
bypass_iommu disabled and add explicit scope data in DMAR drhd structure.

/mnt/sdb/wxg/qemu-next/qemu/build/x86_64-softmmu/qemu-system-x86_64 \
 -machine q35,accel=kvm,default_bus_bypass_iommu=true \
 -cpu host \
 -m 16G \
 -smp 36,sockets=2,cores=18,threads=1 \
 -device pxb-pcie,bus_nr=0x10,id=pci.10,bus=pcie.0,addr=0x3 \
 -device pxb-pcie,bus_nr=0x20,id=pci.20,bus=pcie.0,addr=0x4,bypass_iommu=true \
 -device pcie-root-port,port=0x1,chassis=1,id=pci.11,bus=pci.10,addr=0x0 \
 -device pcie-root-port,port=0x2,chassis=2,id=pci.21,bus=pci.20,addr=0x0 \
 -device virtio-scsi-pci,id=scsi0,bus=pci.11,addr=0x0 \
 -device virtio-scsi-pci,id=scsi1,bus=pci.21,addr=0x0 \
 -drive file=/mnt/sdb/wxg/fedora-48g.qcow2,format=qcow2,if=none,id=drive-scsi0-0-0-0,cache=none,aio=native \
 -device scsi-hd,bus=scsi1.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1 \
 -device intel-iommu \
 -nographic \

And we get the guest configuration:

~ lspci -vt
-+-[0000:20]---00.0-[21]----00.0  Red Hat, Inc. Virtio SCSI
 +-[0000:10]---00.0-[11]----00.0  Red Hat, Inc. Virtio SCSI
 \-[0000:00]-+-00.0  Intel Corporation 82G33/G31/P35/P31 Express DRAM Controller
             +-01.0  Device 1234:1111
             +-02.0  Intel Corporation 82574L Gigabit Network Connection
             +-03.0  Red Hat, Inc. QEMU PCIe Expander bridge
             +-04.0  Red Hat, Inc. QEMU PCIe Expander bridge
             +-1f.0  Intel Corporation 82801IB (ICH9) LPC Interface Controller
             +-1f.2  Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6 port SATA Controller [AHCI mode]
             \-1f.3  Intel Corporation 82801I (ICH9 Family) SMBus Controller

With bypass_iommu enabled on root bus, the attached devices will bypass iommu:

/sys/class/iommu/dmar0
├── devices
│   ├── 0000:10:00.0 -> ../../../../pci0000:10/0000:10:00.0
│   └── 0000:11:00.0 -> ../../../../pci0000:10/0000:10:00.0/0000:11:00.0

Signed-off-by: Xingang Wang <wangxingang5@huawei.com>
Message-Id: <1625748919-52456-8-git-send-email-wangxingang5@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>