Re: [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS

Liuxiangdong (Aven, Cloud Infrastructure Service Product Dept.)
2021-01-25T14:53:10Z

Thanks for replying,

On 2021/1/25 10:41, Like Xu wrote:
> + kvm@vger.kernel.org
>
> Hi Liuxiangdong,
>
> On 2021/1/22 18:02, Liuxiangdong (Aven, Cloud Infrastructure Service
> Product Dept.) wrote:
>> Hi Like,
>>
>> Some questions about
>> https://lore.kernel.org/kvm/20210104131542.495413-1-like.xu@linux.intel.com/
>> <https://lore.kernel.org/kvm/20210104131542.495413-1-like.xu@linux.intel.com/>
>>
>
> Thanks for trying the PEBS feature in the guest,
> and I assume you have correctly applied the QEMU patches for guest PEBS.
>
Is there any other patch that needs to be apply? I use qemu 5.2.0.
(download from github on January 14th)

>> 1)Test in IceLake
>
> In the [PATCH v3 10/17] KVM: x86/pmu: Expose CPUIDs feature bits PDCM,
> DS, DTES64, we only support Ice Lake with the following x86_model(s):
>
> #define INTEL_FAM6_ICELAKE_X 0x6A
> #define INTEL_FAM6_ICELAKE_D 0x6C
>
> you can check the eax output of "cpuid -l 1 -1 -r",
> for example "0x000606a4" meets this requirement.
It's INTEL_FAM6_ICELAKE_X
cpuid -l 1 -1 -r

CPU:
0x00000001 0x00: eax=0x000606a6 ebx=0xb4800800 ecx=0x7ffefbf7
edx=0xbfebfbff

>>
>> HOST:
>>
>> CPU family: 6
>>
>> Model: 106
>>
>> Model name: Intel(R) Xeon(R) Platinum 8378A CPU
>> $@ $@
>>
>> microcode: sig=0x606a6, pf=0x1, revision=0xd000122
>
> As long as you get the latest BIOS from the provider,
> you may check 'cat /proc/cpuinfo | grep code | uniq' with the latest one.
OK. I'll do it later.
>
>>
>> Guest: linux kernel 5.11.0-rc2
>
> I assume it's the "upstream tag v5.11-rc2" which is fine.
Yes.
>
>>
>> We can find pebs/intel_pt flag in guest cpuinfo, but there still
>> exists error when we use perf
>
> Just a note, intel_pt and pebs are two features and we can write
> pebs records to intel_pt buffer with extra hardware support.
> (by default, pebs records are written to the pebs buffer)
>
> You may check the output of "dmesg | grep PEBS" in the guest
> to see if the guest PEBS cpuinfo is exposed and use "perf record
> –e cycles:pp" to see if PEBS feature actually works in the guest.

I apply only pebs patch set to linux kernel 5.11.0-rc2, test perf in
guest and dump stack when return -EOPNOTSUPP

(1)
# perf record -e instructions:pp
Error:
instructions:pp: PMU Hardware doesn't support
sampling/overflow-interrupts. Try 'perf stat'

[ 117.793266] Call Trace:
[ 117.793270] dump_stack+0x57/0x6a
[ 117.793275] intel_pmu_setup_lbr_filter+0x137/0x190
[ 117.793280] intel_pmu_hw_config+0x18b/0x320
[ 117.793288] hsw_hw_config+0xe/0xa0
[ 117.793290] x86_pmu_event_init+0x8e/0x210
[ 117.793293] perf_try_init_event+0x40/0x130
[ 117.793297] perf_event_alloc.part.22+0x611/0xde0
[ 117.793299] ? alloc_fd+0xba/0x180
[ 117.793302] __do_sys_perf_event_open+0x1bd/0xd90
[ 117.793305] do_syscall_64+0x33/0x40
[ 117.793308] entry_SYSCALL_64_after_hwframe+0x44/0xa9

Do we need lbr when we use pebs?

I tried to apply lbr patch
set(https://lore.kernel.org/kvm/911adb63-ba05-ea93-c038-1c09cff15eda@intel.com/)
to kernel and qemu, but there is still other problem.
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument)
for event
...

(2)
# perf record -e instructions:ppp
Error:
instructions:ppp: PMU Hardware doesn't support
sampling/overflow-interrupts. Try 'perf stat'

[ 115.188498] Call Trace:
[ 115.188503] dump_stack+0x57/0x6a
[ 115.188509] x86_pmu_hw_config+0x1eb/0x220
[ 115.188515] intel_pmu_hw_config+0x13/0x320
[ 115.188519] hsw_hw_config+0xe/0xa0
[ 115.188521] x86_pmu_event_init+0x8e/0x210
[ 115.188524] perf_try_init_event+0x40/0x130
[ 115.188528] perf_event_alloc.part.22+0x611/0xde0
[ 115.188530] ? alloc_fd+0xba/0x180
[ 115.188534] __do_sys_perf_event_open+0x1bd/0xd90
[ 115.188538] do_syscall_64+0x33/0x40
[ 115.188541] entry_SYSCALL_64_after_hwframe+0x44/0xa9

This is beacuse x86_pmu.intel_cap.pebs_format is always 0 in
x86_pmu_max_precise().

We rdmsr MSR_IA32_PERF_CAPABILITIES(0x00000345) from HOST, it's f4c5.
From guest, it's 2000

>>
>> # perf record –e cycles:pp
>>
>> Error:
>>
>> cycles:pp: PMU Hardware doesn’t support sampling/overflow-interrupts.
>> Try ‘perf stat’
>>
>> Could you give some advice?
>
> If you have more specific comments or any concerns, just let me know.
>
>>
>> 2)Test in Skylake
>>
>> HOST:
>>
>> CPU family: 6
>>
>> Model: 85
>>
>> Model name: Intel(R) Xeon(R) Gold 6146 CPU @
>>
>> 3.20GHz
>>
>> microcode : 0x2000064
>>
>> Guest: linux 4.18
>>
>> we cannot find intel_pt flag in guest cpuinfo because
>> cpu_has_vmx_intel_pt() return false.
>
> You may check vmx_pebs_supported().
It's true.
>
>>
>> SECONDARY_EXEC_PT_USE_GPA/VM_EXIT_CLEAR_IA32_RTIT_CTL/VM_ENTRY_LOAD_IA32_RTIT_CTL
>> are both disable.
>>
>> Is it because microcode is not supported?
>>
>> And, isthere a new macrocode which can support these bits? How can we
>> get this?
>
> Currently, this patch set doesn't support guest PEBS on the Skylake
> platforms, and if we choose to support it, we will let you know.
>
And now, we want to use pebs in skylake. If we develop based on pebs
patch set, do you have any suggestions?
I think microcode requirements need to be satisfied. Can we use
https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files ?

> ---
> thx,likexu
>
>>
>> Thanks,
>>
>> Liuxiangdong
>>
>
Thanks. Liuxiangdong