From: "Chen, Zide" <zide.chen@intel.com>
To: David Woodhouse <dwmw2@infradead.org>,
Jack Allister <jalliste@amazon.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Sean Christopherson <seanjc@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Shuah Khan <shuah@kernel.org>
Cc: Paul Durrant <paul@xen.org>,
kvm@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 2/2] KVM: selftests: Add KVM/PV clock selftest to prove timer drift correction
Date: Tue, 23 Apr 2024 10:59:21 -0700 [thread overview]
Message-ID: <cdc6c880-c666-4ff2-99f3-56c6b4f7576d@intel.com> (raw)
In-Reply-To: <06864883c53cc4042e1939c04ecbd5ef0f8acf3b.camel@infradead.org>
On 4/23/2024 12:49 AM, David Woodhouse wrote:
>> If I restored the KVM_REQ_GLOBAL_CLOCK_UPDATE request from
>> kvm_arch_vcpu_load(), the selftest works for me, and I ran the test for
>> 1000+ iterations, w/ or w/o TSC scaling, the TEST_ASSERT(delta_corrected
>> <= ±1) never got hit. This is awesome!
>>
>> However, without KVM_REQ_GLOBAL_CLOCK_UPDATE, it still fails on creating
>> a VM. Maybe the init sequence sill needs some rework.
>
> That one confuses me. The crash is actually in debugfs, as it's
> registering the per-vm or per-vcpu stats. I can't imagine *how* that's
> occurring. Or see why the availability of TSC scaling would cause it to
> show up for you and not me. Can I have your .config please?
>
> First thought would be that there's some change in the KVM structures
> and you have some stale object files using the old struct, but then I
> realise I forgot to actually *remove* the now-unused
> kvmclock_update_work from x86's struct kvm_arch anyway.
>
> I'll try to reproduce, as I think I want to *know* what's going on
> here, even if I am going to drop that patch as mentioned in
> https://lore.kernel.org/kvm/a6723ac9e0169839cb33e8022a47c2de213866ac.camel@infradead.org
>
> Are you able to load that vmlinux in gdb and
> (gdb) list *start_creating+0x80
> (gdb) list *kvm_create_vm_debugfs+0x28b
>
> Thanks again.
My apologies, it turns out the KVM_REQ_GLOBAL_CLOCK_UPDATE is not
needed. Today I can't reproduce the issue after removing it. Yesterday
I thought it may miss something related to pfncache.
To be clear, with the above mentioned change to
kvm_scale_tsc(master_tsc_scaling_ratio), the selftest runs reliably
regardless TSC scaling is enabled or not.
next prev parent reply other threads:[~2024-04-23 17:59 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-08 22:07 [PATCH 0/2] Add API to correct KVM/PV clock drift Jack Allister
2024-04-08 22:07 ` [PATCH 1/2] KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for KVM clock drift fixup Jack Allister
2024-04-09 0:34 ` Dongli Zhang
2024-04-09 3:50 ` David Woodhouse
2024-04-10 10:08 ` Allister, Jack
2024-04-08 22:07 ` [PATCH 2/2] KVM: selftests: Add KVM/PV clock selftest to prove timer drift correction Jack Allister
2024-04-09 0:43 ` Dongli Zhang
2024-04-09 4:23 ` David Woodhouse
2024-04-10 10:15 ` Allister, Jack
2024-04-11 13:28 ` David Woodhouse
2024-04-19 17:13 ` Chen, Zide
[not found] ` <17F1A2E9-6BAD-40E7-ACDD-B110CFC124B3@infradead.org>
2024-04-19 18:43 ` David Woodhouse
2024-04-19 23:54 ` Chen, Zide
2024-04-20 10:32 ` David Woodhouse
2024-04-20 16:03 ` David Woodhouse
2024-04-22 22:02 ` Chen, Zide
2024-04-23 7:49 ` David Woodhouse
2024-04-23 17:59 ` Chen, Zide [this message]
2024-04-23 21:02 ` David Woodhouse
2024-04-24 12:58 ` David Woodhouse
2024-04-19 19:34 ` David Woodhouse
2024-04-19 23:53 ` Chen, Zide
2024-04-10 9:52 ` [PATCH v2 0/2] Add API for accurate KVM/PV clock migration Jack Allister
2024-04-10 9:52 ` [PATCH v2 1/2] KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for accurate KVM " Jack Allister
2024-04-10 10:29 ` Paul Durrant
2024-04-10 12:09 ` David Woodhouse
2024-04-10 12:43 ` Paul Durrant
2024-04-17 19:50 ` David Woodhouse
2024-04-15 7:16 ` David Woodhouse
2024-04-10 9:52 ` [PATCH v2 2/2] KVM: selftests: Add KVM/PV clock selftest to prove timer correction Jack Allister
2024-04-10 10:36 ` Paul Durrant
2024-04-12 8:19 ` Dongli Zhang
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