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

Liuxiangdong (Aven, Cloud Infrastructure Service Product Dept.)
2021-01-29T02:53:59Z

On 2021/1/26 15:08, Xu, Like wrote:
> On 2021/1/25 22:47, Liuxiangdong (Aven, Cloud Infrastructure Service
> Product Dept.) wrote:
>> 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)
> Two qemu patches are attached against qemu tree
> (commit 31ee895047bdcf7387e3570cbd2a473c6f744b08)
> and then run the guest with "-cpu,pebs=true".
>
> Note, this two patch are just for test and not finalized for qemu upstream.
Yes, we can use pebs in IceLake when qemu patches applied.
Thanks very much!
>>>> 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
> Yes, it's the target hardware.
>
>> 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
> Yes, you may apply the qemu patches and try it again.
>
>> (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?
> No, lbr ane pebs are two features and we enable it separately.
>
>> 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
>> ...
> We don't need that patch for PEBS feature.
>
>> (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?
> - At least you need to pin guest memory such as "-overcommit mem-lock=true"
> for qemu
> - You may rewrite the patches 13 - 17 for Skylake specific because the
> records format is different with Ice Lake.
OK. So, is there anything else we need to pay attention to except record
format when used for Skylake?
>> I think microcode requirements need to be satisfied. Can we use
>> https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files ?
> You may try it at your risk and again,
> this patch set doesn't support guest PEBS on the Skylake platforms currently.
>
>>> ---
>>> thx,likexu
>>>
>>>> Thanks,
>>>>
>>>> Liuxiangdong
>>>>
>> Thanks. Liuxiangdong
>>