From: Sandipan Das <sandipan.das@amd.com>
To: Jim Mattson <jmattson@google.com>, Like Xu <like.xu.linux@gmail.com>
Cc: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/4] KVM: x86/cpuid: Add AMD CPUID ExtPerfMonAndDbg leaf 0x80000022
Date: Wed, 7 Sep 2022 11:22:54 +0530 [thread overview]
Message-ID: <c07eb8bf-67fc-c645-18f2-cd1623c7a093@amd.com> (raw)
In-Reply-To: <CALMp9eSXTpkKpmqJiS=0NuQOjCFKDeOqjN3wWfyPCBhx-H=Vsw@mail.gmail.com>
On 9/7/2022 9:41 AM, Jim Mattson wrote:
> On Tue, Sep 6, 2022 at 8:59 PM Like Xu <like.xu.linux@gmail.com> wrote:
> [...]
>>>>>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>>>>>> index 75dcf7a72605..08a29ab096d2 100644
>>>>>> --- a/arch/x86/kvm/cpuid.c
>>>>>> +++ b/arch/x86/kvm/cpuid.c
>>>>>> @@ -1094,7 +1094,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>>>>>> entry->edx = 0;
>>>>>> break;
>>>>>> case 0x80000000:
>>>>>> - entry->eax = min(entry->eax, 0x80000021);
>>>>>> + entry->eax = min(entry->eax, 0x80000022);
>>>>>> /*
>>>>>> * Serializing LFENCE is reported in a multitude of ways, and
>>>>>> * NullSegClearsBase is not reported in CPUID on Zen2; help
>>>>>> @@ -1203,6 +1203,25 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>>>>>> if (!static_cpu_has_bug(X86_BUG_NULL_SEG))
>>>>>> entry->eax |= BIT(6);
>>>>>> break;
>>>>>> + /* AMD Extended Performance Monitoring and Debug */
>>>>>> + case 0x80000022: {
>>>>>> + union cpuid_0x80000022_eax eax;
>>>>>> + union cpuid_0x80000022_ebx ebx;
>>>>>> +
>>>>>> + entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
>>>>>> + if (!enable_pmu)
>>>>>> + break;
>>>>>> +
>>>>>> + if (kvm_pmu_cap.version > 1) {
>>>>>> + /* AMD PerfMon is only supported up to V2 in the KVM. */
>>>>>> + eax.split.perfmon_v2 = 1;
>>>>>> + ebx.split.num_core_pmc = min(kvm_pmu_cap.num_counters_gp,
>>>>>> + KVM_AMD_PMC_MAX_GENERIC);
>>>>>
>>>>> Note that the number of core PMCs has to be at least 6 if
>>>>> guest_cpuid_has(vcpu, X86_FEATURE_PERFCTR_CORE). I suppose this leaf
>>>>> could claim fewer, but the first 6 PMCs must work, per the v1 PMU
>>>>> spec. That is, software that knows about PERFCTR_CORE, but not about
>>>>> PMU v2, can rightfully expect 6 PMCs.
>>>>
>>>> I thought the NumCorePmc number would only make sense if
>>>> CPUID.80000022.eax.perfmon_v2
>>>> bit was present, but considering that the user space is perfectly fine with just
>>>> configuring the
>>>> NumCorePmc number without setting perfmon_v2 bit at all, so how about:
>>>
>>> CPUID.80000022H might only make sense if X86_FEATURE_PERFCTR_CORE is
>>> present. It's hard to know in the absence of documentation.
>>
>> Whenever this happens, we may always leave the definition of behavior to the
>> hypervisor.
>
> I disagree. If CPUID.0H reports "AuthenticAMD," then AMD is the sole
> authority on behavior.
>
I understand that official documentation is not out yet. However, for Zen 4
models, it is expected that both the PerfMonV2 bit of CPUID.80000022H EAX and
the PerfCtrExtCore bit of CPUID.80000001H ECX will be set.
>>>
>>>> /* AMD Extended Performance Monitoring and Debug */
>>>> case 0x80000022: {
>>>> union cpuid_0x80000022_eax eax;
>>>> union cpuid_0x80000022_ebx ebx;
>>>> bool perfctr_core;
>>>>
>>>> entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
>>>> if (!enable_pmu)
>>>> break;
>>>>
>>>> perfctr_core = kvm_cpu_cap_has(X86_FEATURE_PERFCTR_CORE);
>>>> if (!perfctr_core)
>>>> ebx.split.num_core_pmc = AMD64_NUM_COUNTERS;
>>>> if (kvm_pmu_cap.version > 1) {
>>>> /* AMD PerfMon is only supported up to V2 in the KVM. */
>>>> eax.split.perfmon_v2 = 1;
>>>> ebx.split.num_core_pmc = min(kvm_pmu_cap.num_counters_gp,
>>>> KVM_AMD_PMC_MAX_GENERIC);
>>>> }
>>>> if (perfctr_core) {
>>>> ebx.split.num_core_pmc = max(ebx.split.num_core_pmc,
>>>> AMD64_NUM_COUNTERS_CORE);
>>>> }
>>>
>>> This still isn't quite right. All AMD CPUs must support a minimum of 4 PMCs.
>>
>> K7 at least. I could not confirm that all antique AMD CPUs have 4 counters w/o
>> perfctr_core.
>
> The APM says, "All implementations support the base set of four
> performance counter / event-select pairs." That is unequivocal.
>
That is true. The same can be inferred from amd_core_pmu_init() in
arch/x86/events/amd/core.c. If PERFCTR_CORE is not detected, it assumes
that the four legacy counters are always available.
- Sandipan
next prev parent reply other threads:[~2022-09-07 5:53 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-05 12:39 [PATCH 0/4] KVM: x86/svm/pmu: Add AMD Guest PerfMonV2 support Like Xu
2022-09-05 12:39 ` [PATCH 1/4] KVM: x86/svm/pmu: Limit the maximum number of supported GP counters Like Xu
2022-09-05 17:26 ` Jim Mattson
2022-09-06 12:38 ` Like Xu
2022-09-05 12:39 ` [PATCH 2/4] KVM: x86/pmu: Make part of the Intel v2 PMU MSRs handling x86 generic Like Xu
2022-09-05 12:39 ` [PATCH 3/4] KVM: x86/svm/pmu: Add AMD PerfMonV2 support Like Xu
2022-09-05 18:00 ` Jim Mattson
2022-09-06 12:45 ` Like Xu
2022-09-06 20:19 ` Jim Mattson
2022-09-07 3:50 ` Like Xu
2022-09-07 4:15 ` Jim Mattson
2022-09-05 12:39 ` [PATCH 4/4] KVM: x86/cpuid: Add AMD CPUID ExtPerfMonAndDbg leaf 0x80000022 Like Xu
2022-09-05 17:36 ` Jim Mattson
2022-09-06 12:53 ` Like Xu
2022-09-06 20:08 ` Jim Mattson
2022-09-07 3:59 ` Like Xu
2022-09-07 4:11 ` Jim Mattson
2022-09-07 5:52 ` Sandipan Das [this message]
2022-09-07 6:39 ` Like Xu
2022-09-08 6:00 ` Sandipan Das
2022-09-08 23:14 ` Jim Mattson
2022-09-05 12:39 ` [kvm-unit-tests PATCH 1/2] x86/pmu: Update rdpmc testcase to cover #GP and emulation path Like Xu
2022-10-05 21:36 ` Sean Christopherson
2022-10-19 8:50 ` Like Xu
2022-09-05 12:39 ` [kvm-unit-tests PATCH 2/2] x86/pmu: Add AMD Guest PerfMonV2 testcases Like Xu
2022-10-05 22:08 ` Sean Christopherson
2022-10-19 9:40 ` Like Xu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=c07eb8bf-67fc-c645-18f2-cd1623c7a093@amd.com \
--to=sandipan.das@amd.com \
--cc=jmattson@google.com \
--cc=kvm@vger.kernel.org \
--cc=like.xu.linux@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=seanjc@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).