This series enhances the current host KVM model with capability to
set writable ID reg fields.
Since v6.7 kernel, KVM/arm allows the userspace to overwrite the values
of a subset of ID regs. The list of writable fields continues to grow.
The feature ID range is defined as the AArch64 System register space
with op0==3, op1=={0, 1, 3}, CRn==0, CRm=={0-7}, op2=={0-7}.
The end goal is to get more flexibility when migrating guests
between different host hardware.
QEMU retrieves the writable ID fields from KVM UAPI [1] and
match them against a generated description of ID regs and their
named fields that stem from AARCHMRS Registers.json file.
Current description is based on latest 2026-03 edition.
The content of the generated files was compared against kernel
linux/arch/arm64/tools/sysreg file. It is not straightforward
to have unit tests for python scripts as there are many cases for
field extraction.
For each writable named field a uint64 property is created
following the "SYSREG_<REG>_<FIELD>" naming convention. REG and
FIELD names are those described in ARM ARM Reference manual.
The list of SYSREG_ID properties can be retrieved through the qmp
monitor using query-cpu-model-expansion [2].
Connie & Eric
This series can be found at:
https://github.com/eauger/qemu/tree/arm-cpu-model-v5
History:
--------
v4 -> v5:
- generate target/arm/cpu-idregs.h.inc that look similar to
the format used in [RFC PATCH v1 02/13] target/arm:
named_cpu_model: Add ID Register Fields without the
description of the value values nor safe policy/value.
I guess valid values could be generated from the Registers.json
file too. Safe policy/values cannot.
I reused one patch from the above series.
Let's see how both series can progress/coexist without any
anticipated bias.
- Addressed all comments from Shameer on v4
- Addressed 2 comments from v4 that were missed including the
issue of IDreg visibility affected by some other settings.
Unfortunately I was not able to test it.
- Further look at overrides between low level id reg field
properties versus legacy CPU options. I have the feeling they
can coexist as long as we document the hierarchy between them:
host kvm default -> ID reg field props -> legacy CPU options
- Noticed more writable fields that are RES0/RAZ
- Improved commit messages in general
References:
-----------
[1]
KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES
KVM_ARM_GET_REG_WRITABLE_MASKS
Documentation/virt/kvm/api.rst
[2]
qemu-system-aarch64 -qmp unix:/home/augere/TEST/QEMU/qmp-sock,server,nowait -M
virt --enable-kvm -cpu custom
sudo build/run qmp-shell /home/augere/TEST/QEMU/qmp-sock
Welcome to the QMP low-level shell!
Connected to QEMU 11.0.50
(QEMU) query-cpu-model-expansion type=full model={"name":"host"}
Cornelia Huck (3):
target/arm/kvm: Introduce kvm_get_writable_id_regs
arm-qmp-cmds: introspection for ID register props
arm/cpu-features: document ID reg properties
Eric Auger (14):
scripts: introduce scripts/update-aarch64-cpu-sysregs-header.py
target/arm/cpu-sysregs.h.inc: Sort by name alphabetical order
target/arm/cpu-sysregs.h.inc: Update with automatic generation
arm/cpu: Add infra to handle generated ID register definitions
scripts: Introduce scripts/aarch64_sysreg_helpers module
scripts: Introduce scripts/update-aarch64-cpu-sysreg-properties.py
target/arm/cpu-idregs.h.inc: generate with script
target/arm/cpu64: Retrieve writable ID reg map in
aarch64_host_initfn()
arm/kvm: Initialize all writable ID registers from host
arm/kvm: write back modified ID regs to KVM
target/arm/kvm: Introduce kvm_arm_expose_idreg_properties
target/arm/kvm: Special case REVIDR_EL1 and AIDR_EL1
target/arm/kvm: Ignore some writable bits that shouldn't be
target/arm/cpu: Expose writable ID reg field properties on the kvm
host vcpu model
Shaju Abraham (1):
target/arm/cpu_idregs: generate tables for Arm64 ID registers and
fields
docs/system/arm/cpu-features.rst | 106 ++-
scripts/aarch64_sysreg_helpers.py | 109 ++++
.../update-aarch64-cpu-sysreg-properties.py | 168 +++++
scripts/update-aarch64-cpu-sysregs-header.py | 51 ++
target/arm/arm-qmp-cmds.c | 19 +
target/arm/cpu-idregs.c | 50 ++
target/arm/cpu-idregs.h | 33 +
target/arm/cpu-idregs.h.inc | 617 ++++++++++++++++++
target/arm/cpu-sysregs.h.inc | 57 +-
target/arm/cpu.h | 3 +
target/arm/cpu64.c | 14 +
target/arm/kvm-stub.c | 5 +
target/arm/kvm.c | 320 ++++++++-
target/arm/kvm_arm.h | 12 +
target/arm/meson.build | 1 +
target/arm/trace-events | 6 +
16 files changed, 1539 insertions(+), 32 deletions(-)
create mode 100644 scripts/aarch64_sysreg_helpers.py
create mode 100644 scripts/update-aarch64-cpu-sysreg-properties.py
create mode 100755 scripts/update-aarch64-cpu-sysregs-header.py
create mode 100644 target/arm/cpu-idregs.c
create mode 100644 target/arm/cpu-idregs.h
create mode 100644 target/arm/cpu-idregs.h.inc
--
2.53.0
