mirror of
https://github.com/xemu-project/xemu.git
synced 2024-11-26 21:10:42 +00:00
732de3e72d
Signed-off-by: Xingang Wang <wangxingang5@huawei.com> Message-Id: <1625748919-52456-10-git-send-email-wangxingang5@huawei.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
90 lines
3.6 KiB
Plaintext
90 lines
3.6 KiB
Plaintext
BYPASS IOMMU PROPERTY
|
|
=====================
|
|
|
|
Description
|
|
===========
|
|
Traditionally, there is a global switch to enable/disable vIOMMU. All
|
|
devices in the system can only support go through vIOMMU or not, which
|
|
is not flexible. We introduce this bypass iommu property to support
|
|
coexist of devices go through vIOMMU and devices not. This is useful to
|
|
passthrough devices with no-iommu mode and devices go through vIOMMU in
|
|
the same virtual machine.
|
|
|
|
PCI host bridges have a bypass_iommu property. This property is used to
|
|
determine whether the devices attached on the PCI host bridge will bypass
|
|
virtual iommu. The bypass_iommu property is valid only when there is a
|
|
virtual iommu in the system, it is implemented to allow some devices to
|
|
bypass vIOMMU. When bypass_iommu property is not set for a host bridge,
|
|
the attached devices will go through vIOMMU by default.
|
|
|
|
Usage
|
|
=====
|
|
The bypass iommu feature support PXB host bridge and default main host
|
|
bridge, we add a bypass_iommu property for PXB and default_bus_bypass_iommu
|
|
for machine. Note that default_bus_bypass_iommu is available only when
|
|
the 'q35' machine type on x86 architecture and the 'virt' machine type
|
|
on AArch64. Other machine types do not support bypass iommu for default
|
|
root bus.
|
|
|
|
1. The following is the bypass iommu options:
|
|
(1) PCI expander bridge
|
|
qemu -device pxb-pcie,bus_nr=0x10,addr=0x1,bypass_iommu=true
|
|
(2) Arm default host bridge
|
|
qemu -machine virt,iommu=smmuv3,default_bus_bypass_iommu=true
|
|
(3) X86 default root bus bypass iommu:
|
|
qemu -machine q35,default_bus_bypass_iommu=true
|
|
|
|
2. Here is the detailed qemu command line for 'virt' machine with PXB on
|
|
AArch64:
|
|
|
|
qemu-system-aarch64 \
|
|
-machine virt,kernel_irqchip=on,iommu=smmuv3,default_bus_bypass_iommu=true \
|
|
-device pxb-pcie,bus_nr=0x10,id=pci.10,bus=pcie.0,addr=0x3.0x1 \
|
|
-device pxb-pcie,bus_nr=0x20,id=pci.20,bus=pcie.0,addr=0x3.0x2,bypass_iommu=true \
|
|
|
|
And we got:
|
|
- a default host bridge which bypass SMMUv3
|
|
- a pxb host bridge which go through SMMUv3
|
|
- a pxb host bridge which bypass SMMUv3
|
|
|
|
3. Here is the detailed qemu command line for 'q35' machine with PXB on
|
|
x86 architecture:
|
|
|
|
qemu-system-x86_64 \
|
|
-machine q35,accel=kvm,default_bus_bypass_iommu=true \
|
|
-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 intel-iommu \
|
|
|
|
And we got:
|
|
- a default host bridge which bypass iommu
|
|
- a pxb host bridge which go through iommu
|
|
- a pxb host bridge which bypass iommu
|
|
|
|
Limitations
|
|
===========
|
|
There might be potential security risk when devices bypass iommu, because
|
|
devices might send malicious dma request to virtual machine if there is no
|
|
iommu isolation. So it would be necessary to only bypass iommu for trusted
|
|
device.
|
|
|
|
Implementation
|
|
==============
|
|
The bypass iommu feature includes:
|
|
- Address space
|
|
Add bypass iommu property check of PCI Host and do not get iommu address
|
|
space for devices bypass iommu.
|
|
- Arm SMMUv3 support
|
|
We traverse all PCI root bus and get bus number ranges, then build explicit
|
|
RID mapping for devices which do not bypass iommu.
|
|
- X86 IOMMU support
|
|
To support Intel iommu, we traverse all PCI host bridge and get information
|
|
of devices which do not bypass iommu, then fill the DMAR drhd struct with
|
|
explicit device scope info. To support AMD iommu, add check of bypass iommu
|
|
when traverse the PCI hsot bridge.
|
|
- Machine and PXB options
|
|
We add bypass iommu options in machine option for default root bus, and add
|
|
option for PXB also. Note that the default value of bypass iommu is false,
|
|
so that the devices will by default go through iommu if there exist one.
|
|
|