Hi Igor,
On 2021/6/8 21:38, Igor Mammedov wrote:
On Tue, 8 Jun 2021 20:24:35 +0800
Xingang Wang <wangxinga...@huawei.com> wrote:
Hi Igor,
On 2021/6/5 20:32, Igor Mammedov wrote:
On Tue, 25 May 2021 03:49:57 +0000
Wang Xingang <wangxinga...@huawei.com> wrote:
From: Xingang Wang <wangxinga...@huawei.com>
These patches add support for configure bypass_iommu on/off for
pci root bus, including primary bus and pxb root bus. At present,
all root bus will go through iommu when iommu is configured,
which is not flexible, because in many situations the need for using
iommu and bypass iommu aften exists at the same time.
'many situations' doesn't describe why bypass is needed,
can you provide a use-cases here and what are security implications
when bypass is allowed.
(PS: the later probably should be documented somewhere in the docs/option
description)
It is possible that some devices support the iommu and some devices do
not. When we need to pass through both kind of devices to a virtual
machine, bypass iommu would help.
E.g I have a HiSilicon network and computing encryption device(SEC),
which supports both iommu and noiommu mode. If I have to use a SEC in
noiommu mode along with another device which need iommu, then it would
need this bypass iommu feature.
Besides, bypass iommu would have less performance loss because there
might be many trap in and out using a virtual iommu.
usually if one enables 'iommu', one wants the isolation it provides.
so the bypass option negates that. Why not just use machine with IOMMU
disabled globally in the first place?
I am considering the situation that devices with IOMMU enabled and
devices with IOMMU disabled are used at the same time. Right now there's
only one global switch to check whether IOMMU will be used, which is
not flexible for this kind of usage.
To keep consistent with previous usages with global IOMMU switch
enabled, IOMMU is enabled by default if no bypass option is set.
However there might be potential security risks without iommu,
as devices might send malicious dma requests.
It would be necessary to only bypass iommu for trusted devices.
that's what I was worried about, at least it should be documented
or a warning printed to discourage using the feature.
Thanks for your suggestions, I will try to add enough explanation in
docs and add warning for usage of iommu bypass.
Thanks
Xingang
So this add option to enable/disable bypass_iommu for primary bus
and pxb root bus. The bypass_iommu property is set to false default,
meaning that devcies will go through iommu if no explicit configuration
is added. When bypass_iommu is enabled for the root bus, devices
attached to it will bypass iommu, otherwise devices will go through
iommu.
This feature can be used in this manner:
arm: -machine virt,iommu=smmuv3,bypass_iommu=true
x86: -machine q35,bypass_iommu=true
pxb: -device pxb-pcie,bus_nr=0x10,id=pci.10,bus=pcie.0,bypass_iommu=true
History:
v3 -> v4:
- simplify the logic in building the IORT idmap
v2 -> v3:
- rebase on top of v6.0.0-rc4
- Took into account Eric's comments, replace with a bypass_iommu
proerty
- When building the IORT idmap, cover the whole RID space
v1 -> v2:
- rebase on top of v6.0.0-rc0
- Fix some issues
- Took into account Eric's comments, and remove the PCI_BUS_IOMMU flag,
replace it with a property in PCIHostState.
- Add support for x86 iommu option
Xingang Wang (8):
hw/pci/pci_host: Allow bypass iommu for pci host
hw/pxb: Add a bypass iommu property
hw/arm/virt: Add a machine option to bypass iommu for primary bus
hw/i386: Add a pc machine option to bypass iommu for primary bus
hw/pci: Add pci_bus_range to get bus number range
hw/arm/virt-acpi-build: Add explicit IORT idmap for smmuv3 node
hw/i386/acpi-build: Add explicit scope in DMAR table
hw/i386/acpi-build: Add bypass_iommu check when building IVRS table
hw/arm/virt-acpi-build.c | 135 ++++++++++++++++++++++++----
hw/arm/virt.c | 26 ++++++
hw/i386/acpi-build.c | 70 ++++++++++++++-
hw/i386/pc.c | 18 ++++
hw/pci-bridge/pci_expander_bridge.c | 3 +
hw/pci-host/q35.c | 1 +
hw/pci/pci.c | 33 ++++++-
hw/pci/pci_host.c | 2 +
include/hw/arm/virt.h | 1 +
include/hw/i386/pc.h | 1 +
include/hw/pci/pci.h | 2 +
include/hw/pci/pci_host.h | 1 +
12 files changed, 270 insertions(+), 23 deletions(-)
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