Currently, QEMU supports emulating either stage-1 or stage-2 SMMUs
but not nested instances.
This patch series adds support for nested translation in SMMUv3,
this is controlled by property “arm-smmuv3.stage=nested”, and
advertised to guests as (IDR0.S1P == 1 && IDR0.S2P == 2)
Main changes(architecture):
============================
1) CDs are considered IPA and translated with stage-2.
2) TTBx and tables for stage-1 are considered IPA and translated
with stage-2.
3) Translate the IPA address with stage-2.
TLBs:
======
TLBs are the most tricky part.
1) General design
Unified(Combined) design is used, where a new tag is added "stage"
which has 2 valid values:
- STAGE_1: Meaning this entry translates VA to PADDR, it can be
cached from fully nested configuration or from stage-1 only.
It doesn't support separate cached entries (VA to IPA).
- STAGE_2: Meaning this translates IPA to PADDR, cached from
stage-2 only configuration.
TLBs are also modified to cache 2 permissions, a new permission added
"parent_perm."
For non-nested configuration, perm == parent_perm and nothing
changes. This is used to know which stage to use in case there is
a permission fault from a TLB entry.
2) Caching in TLB
Stage-1 and stage-2 are inserted in the TLB as is.
For nested translation, both entries are combined into one TLB
entry. Everything is used from stage-1, except:
- transatled_addr from stage-2.
- parent_perm is from stage-2.
- addr_mask: is the minimum of both.
3) TLB Lookup
For stage-1 and nested translations, it look for STAGE_1 entries.
For stage-2 it look for STAGE_2 TLB entries.
4) TLB invalidation
- Stage-1 commands (CMD_TLBI_NH_VAA, SMMU_CMD_TLBI_NH_VA,
SMMU_CMD_TLBI_NH_ALL): Invalidate TLBs tagged with SMMU_STAGE_1.
- Stage-2 commands (CMD_TLBI_S2_IPA): Invalidate TLBs tagged with
SMMU_STAGE_2.
- All (SMMU_CMD_TLBI_S12_VMALL): Will invalidate both, this is
communicated to the TLB as SMMU_NESTED which is (SMMU_STAGE_1 |
SMMU_STAGE_2) which uses it as a mask.
As far as I understand, this is compliant with the ARM
architecture, based on:
- ARM ARM DDI 0487J.a: RLGSCG, RTVTYQ, RGNJPZ
- ARM IHI 0070F.b: 16.2 Caching
An alternative approach would be to instantiate 2 TLBs, one per
each stage. I haven’t investigated that.
Others
=======
- Advertise SMMUv3.2-S2FWB, it is NOP for QEMU as it doesn’t support
attributes.
- OAS: A typical setup with nesting is to share CPU stage-2 with the
SMMU, and according to the user manual, SMMU OAS must match the
system physical address.
This was discussed before in
https://lore.kernel.org/all/20230226220650.1480786-11-smost...@google.com/
The implementation here, follows the discussion, where migration is
added and oas is set up from the board (virt). However, the OAS is
chosen based on the CPU PARANGE as there is no fixed one.
- For nested configuration, IOVA notifier only notifies for stage-1
invalidations (as far as I understand this is the intended
behaviour as it notifies for IOVA)
- Stop ignoring VMID for stage-1 if stage-2 is also supported.
Future improvements:
=====================
1) One small improvement, that I don’t think it’s worth the extra
complexity, is in case of Stage-1 TLB miss for nested translation,
we can do stage-1 walk and lookup for stage-2 TLBs, instead of
doing the full walk.
2) Patch 0006 (hw/arm/smmuv3: Translate CD and TT using stage-2 table)
introduces a macro to use functions that rely on cfg for stage-2,
I don’t like it. However, I didn’t find a simple way around it,
either we change many functions to have a separate stage argument,
or add another arg in config, which is probably more code.
Testing
========
1) IOMMUFD + VFIO
Kernel: https://lore.kernel.org/all/cover.1683688960.git.nicol...@nvidia.com/
VMM:
https://qemu-devel.nongnu.narkive.com/o815DqpI/rfc-v5-0-8-arm-smmuv3-emulation-support
By assigning
“virtio-net-pci,netdev=net0,disable-legacy=on,iommu_platform=on,ats=on”,
to a guest VM (on top of QEMU guest) with VIFO and IOMMUFD.
2) Work in progress prototype I am hacking on for nesting on KVM
(this is nowhere near complete, and misses many stuff but it
doesn't require VMs/VFIO) also with virtio-net-pci and git
cloning a bunch of stuff and also observing traces.
https://android-kvm.googlesource.com/linux/+log/refs/heads/smostafa/android15-6.6-smmu-nesting-wip
hw/arm/smmuv3: Split smmuv3_translate() better viewed with --color-moved
Mostafa Saleh (12):
hw/arm/smmu: Use enum for SMMU stage
hw/arm/smmu: Split smmuv3_translate()
hw/arm/smmu: Add stage to TLB
hw/arm/smmu: Support nesting in commands
hw/arm/smmuv3: Support nested SMMUs in smmuv3_notify_iova()
hw/arm/smmuv3: Translate CD and TT using stage-2 table
hw/arm/smmu-common: Support nested translation
hw/arm/smmuv3: Support and advertise nesting
hw/arm/smmuv3: Advertise S2FWB
hw/arm/smmu: Refactor SMMU OAS
hw/arm/smmuv3: Add property for OAS
hw/arm/virt: Set SMMU OAS based on CPU PARANGE
hw/arm/smmu-common.c | 256 ++++++++++++++++++----
hw/arm/smmu-internal.h | 2 +
hw/arm/smmuv3-internal.h | 17 +-
hw/arm/smmuv3.c | 405 ++++++++++++++++++++++-------------
hw/arm/trace-events | 14 +-
hw/arm/virt.c | 14 +-
include/hw/arm/smmu-common.h | 46 +++-
include/hw/arm/smmuv3.h | 1 +
target/arm/cpu.h | 2 +
target/arm/cpu64.c | 5 +
10 files changed, 533 insertions(+), 229 deletions(-)
--
2.44.0.396.g6e790dbe36-goog
