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Re: [RFC PATCH 0/3] Add API for list cpu extensions
From: |
Daniel Henrique Barboza |
Subject: |
Re: [RFC PATCH 0/3] Add API for list cpu extensions |
Date: |
Fri, 25 Aug 2023 11:15:42 -0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 |
Hi Zhiwei! I have two observations:
- this API doesn't play well with KVM as is. In a KVM environment, asking for
the
enabled extensions of the 'host' CPU returns:
$ ./mnt/qemu/bin/qemu-system-riscv64 -cpu host,help
Enable extension:
rv64imafdch_zicbom_zicboz_zicsr_zifencei_zihintntl_zihintpause_zawrs_zfa_zba_zbb_zbc_zbs_sstc_svadu
This is the same set of extensions enabled in the 'rv64' CPU for TCG. This is
happening because they're sharing the same code that creates properties.
If I apply these patches on top of the "split TCG/KVM accelerators from cpu.c" I
sent earlier, this happens:
$ ./mnt/qemu/bin/qemu-system-riscv64 -cpu host,help
Enable extension:
rv64
For TCG only CPUs (vendor CPUs) the API works even on a KVM host, regardless of
applying on top of riscv-to-apply.next or those accel patches:
$ ./mnt/qemu/bin/qemu-system-riscv64 -cpu veyron-v1,help
Enable extension:
rv64ch_zicbom_zicboz_zicsr_zifencei_zba_zbb_zbc_zbs_smaia_smstateen_ssaia_sscofpmf_sstc_svinval_svnapot_svpbmt_xventanacondops
It seems to me that 'cpu help' doesn't engage the KVM driver accel_init()
function.
If we decide to go ahead with this API we'll need to either figure out if
accel-specific
initialization is possible. If not, we should declare that this API works only
for TCG.
- I think the presence of the 'cpu help' API limits the command line parsing
altogether,
making cheeky things like this possible:
(disabling extensions in the cmd line and asking the extensions)
$ ./build/qemu-system-riscv64 -cpu veyron-v1,icbom=false,icboz=false,help
Enable extension:
rv64ch_zicbom_zicboz_zicsr_zifencei_zba_zbb_zbc_zbs_smaia_smstateen_ssaia_sscofpmf_sstc_svinval_svnapot_svpbmt_xventanacondops
(silly option ignored)
$ ./build/qemu-system-riscv64 -cpu veyron-v1,lalala=true,help
Enable extension:
rv64ch_zicbom_zicboz_zicsr_zifencei_zba_zbb_zbc_zbs_smaia_smstateen_ssaia_sscofpmf_sstc_svinval_svnapot_svpbmt_xventanacondops
This is not a gamebreaker but something to keep in mind when using this API.
Thanks,
Daniel
On 8/25/23 09:16, LIU Zhiwei wrote:
Some times we want to know what is the really mean of one cpu option.
For example, in RISC-V, we usually specify a cpu in this way:
-cpu rv64,v=on
If we don't look into the source code, we can't get the ISA extensions
of this -cpu command line.
In this patch set, we add one list_cpu_props API for common cores. It
will output the enabled ISA extensions.
In the near future, I will also list all possible user configurable
options and all possible extensions for this cpu.
In order to reuse the options parse code, I also add a QemuOptsList
for cpu.
After this patch, we can output the extensions for cpu,
"""
./qemu-system-riscv64 -cpu rv64,help
Enable extension:
rv64imafdch_zicbom_zicboz_zicsr_zifencei_zihintpause_zawrs_zfa_zba_zbb_zbc_zbs_sstc_svadu
"""
Notice currently this patch is only working for RISC-V system mode.
Thanks Andrew Jones for your suggestion!
Todo:
1) Output all possible user configurable options and all extensions.
2) Add support for RISC-V linux-user mode
3) Add support for other archs
LIU Zhiwei (3):
cpu: Add new API cpu_type_by_name
target/riscv: Add API list_cpu_props
softmmu/vl: Add qemu_cpu_opts QemuOptsList
cpu.c | 39 +++++++++++++++++++++++++++------------
include/exec/cpu-common.h | 1 +
include/hw/core/cpu.h | 11 +++++++++++
softmmu/vl.c | 35 +++++++++++++++++++++++++++++++++++
target/riscv/cpu.c | 10 ++++++++++
target/riscv/cpu.h | 2 ++
6 files changed, 86 insertions(+), 12 deletions(-)