Re: [PATCH 0/7] target/arm: Add vSPE support to KVM guest

[Andrew Jones]

On Fri, Aug 07, 2020 at 08:10:30AM +0000, Haibo Xu wrote:
> This series add support for SPE(Statistical Profiling Extension)[1]
> in KVM guest. It's based on Andrew Murray's kernel KVM patches V2[2],
> and has been tested to ensure that guest can use SPE with valid data.
> E.g.
> 
> In host:
> $ ./qemu-system-aarch64 \
>         -cpu host -M virt,accel=kvm,gic-version=3 -nographic -m 2048M \
>         -kernel ./Image-new \
>         -initrd /boot/initrd.img-5.6.0-rc2+ \
>         -append "root=/dev/vda rw console=ttyAMA0" -nodefaults -serial stdio\
>         -drive if=none,file=./xenial.rootfs.ext4,id=hd0,format=raw \
>         -device virtio-blk-device,drive=hd0  \
> 
> In guest:
> $ perf record -e arm_spe/ts_enable=1,pa_enable=1,pct_enable=1/ \
>         dd if=/dev/zero of=/dev/null count=1000
> $ perf report --dump-raw-trace > spe_buf.txt
> 
> The spe_buf.txt should contain similar data as below:
> 
> . ... ARM SPE data: size 135944 bytes
> .  00000000:  b0 f4 d3 29 10 00 80 ff a0                      PC 
> 0xff80001029d3f4 el1 ns=1
> .  00000009:  99 0b 00                                        LAT 11 ISSUE
> .  0000000c:  98 0d 00                                        LAT 13 TOT
> .  0000000f:  52 16 00                                        EV RETIRED 
> L1D-ACCESS TLB-ACCESS
> .  00000012:  49 00                                           LD
> .  00000014:  b2 d0 40 d8 70 00 00 ff 00                      VA 
> 0xff000070d840d0
> .  0000001d:  9a 01 00                                        LAT 1 XLAT
> .  00000020:  00 00 00                                        PAD
> .  00000023:  71 a5 1f b3 20 14 00 00 00                      TS 86447955877
> .  0000002c:  b0 7c f9 29 10 00 80 ff a0                      PC 
> 0xff80001029f97c el1 ns=1
> .  00000035:  99 02 00                                        LAT 2 ISSUE
> .  00000038:  98 03 00                                        LAT 3 TOT
> .  0000003b:  52 02 00                                        EV RETIRED
> .  0000003e:  48 00                                           INSN-OTHER
> .  00000040:  00 00 00                                        PAD
> .  00000043:  71 ef 1f b3 20 14 00 00 00                      TS 86447955951
> .  0000004c:  b0 f0 e9 29 10 00 80 ff a0                      PC 
> 0xff80001029e9f0 el1 ns=1
> .  00000055:  99 02 00                                        LAT 2 ISSUE
> .  00000058:  98 03 00                                        LAT 3 TOT
> .  0000005b:  52 02 00                                        EV RETIRED
> 
> If you want to disable the vSPE support, you can use the 'spe=off' cpu
> property:
> 
> ./qemu-system-aarch64 \
>         -cpu host,spe=off -M virt,accel=kvm,gic-version=3 -nographic -m 2048M 
> \
>         -kernel ./Image-new \
>         -initrd /boot/initrd.img-5.6.0-rc2+ \
>         -append "root=/dev/vda rw console=ttyAMA0" -nodefaults -serial stdio\
>         -drive if=none,file=./xenial.rootfs.ext4,id=hd0,format=raw \
>         -device virtio-blk-device,drive=hd0  \
> 
> Note:
> (1) Since the kernel patches are still under review, some of the macros
>     in the header files may be changed after merging. We may need to
>     update them accordingly.
> (2) These patches only add vSPE support in KVM mode, for TCG mode, I'm
>     not sure whether we need to support it.
> (3) Just followed the 'pmu' property, we only allow this feature to be
>     removed from CPUs which enable it by default. But since the SPE is
>     an optional feature extension for Armv8.2, I think a better way may
>     be to disable it by default, and only enable it when the host cpu
>     do have the feature.

* When not using KVM, if TCG supports SPE emulation, then it should be
  enabled by default with '-cpu max'.

* When using KVM, if KVM supports the feature, then it should be enabled
  by default with '-cpu max' or '-cpu host' (which are currently the only
  ways to use KVM on AArch64)

* When using KVM, if KVM does not support the feature (either the CPU
  doesn't support it, or the version of KVM in use doesn't know what to
  do with it), then the feature should obviously be disabled for the VM
  by default, since there's no way to enable it.

> 
> [1]https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/
>    posts/statistical-profiling-extension-for-armv8-a
> [2]https://www.spinics.net/lists/arm-kernel/msg776228.html
> 
> Haibo Xu (7):
>   update Linux headers with new vSPE macros
>   target/arm/kvm: spe: Add helper to detect SPE when using KVM
>   target/arm/cpu: spe: Add an option to turn on/off vSPE support
>   target/arm/kvm: spe: Unify device attr operatioin helper
>   target/arm/kvm: spe: Add device init and set_irq operations
>   hw/arm/virt: spe: Add SPE fdt binding for virt machine
>   target/arm/cpu: spe: Enable spe to work with host cpu
> 
>  hw/arm/virt-acpi-build.c      |  3 +++
>  hw/arm/virt.c                 | 42 ++++++++++++++++++++++++++++++
>  include/hw/acpi/acpi-defs.h   |  1 +
>  include/hw/arm/virt.h         |  1 +
>  linux-headers/asm-arm64/kvm.h |  4 +++
>  linux-headers/linux/kvm.h     |  2 ++
>  target/arm/cpu.c              | 34 +++++++++++++++++++++++++
>  target/arm/cpu.h              |  5 ++++
>  target/arm/kvm.c              | 11 ++++++++
>  target/arm/kvm64.c            | 48 ++++++++++++++++++++++++++++++++---
>  target/arm/kvm_arm.h          | 18 +++++++++++++

This series should also be updating these files:

 docs/system/arm/cpu-features.rst
 target/arm/monitor.c
 tests/qtest/arm-cpu-features.c

Thanks,
drew

>  11 files changed, 166 insertions(+), 3 deletions(-)
> 
> -- 
> 2.17.1
> 
>