linux-kernel - Re: [PATCH v3 0/9] Parallel CPU bringup for x86

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Date:   Tue, 21 Dec 2021 22:33:04 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Igor Mammedov <imammedo@...hat.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "mimoja@...oja.de" <mimoja@...oja.de>,
        "hewenliang4@...wei.com" <hewenliang4@...wei.com>,
        "hushiyuan@...wei.com" <hushiyuan@...wei.com>,
        "luolongjun@...wei.com" <luolongjun@...wei.com>,
        "hejingxian@...wei.com" <hejingxian@...wei.com>
Subject: Re: [PATCH v3 0/9] Parallel CPU bringup for x86_64



On 21 December 2021 22:25:35 GMT, Tom Lendacky <thomas.lendacky@....com> wrote:
>On 12/20/21 3:47 PM, Tom Lendacky wrote:
>> On 12/20/21 3:29 PM, David Woodhouse wrote:
>>> On Mon, 2021-12-20 at 12:54 -0600, Tom Lendacky wrote:
>>>> Took the tree back to commit df9726cb7178 and then applied this change.
>>>> I'm unable to trigger any kind of failure with this change.
>>>
>>> Hm... I fired up an EC2 m6a.48xlarge instance (192 CPUs) to play with.
>>>
>>> I can reproduce your triple-fault on SMP bringup, but only with kexec.
>>> And I basically can't get *anything* to kexec without that triple-
>>> fault. Not a clean 5.16-rc2, not the Fedora stock 5.14.10 kernel.
>>>
>>> If I *boot* instead of kexec, I have not yet seen the problem at all.
>>> This is using Legacy BIOS not UEFI.
>> 
>> Let me try with a legacy BIOS and see if I can repro. Might not be until 
>> tomorrow, though, since I had to let someone borrow the machine.
>
>I still encounter the issue using a legacy BIOS (SeaBIOS).

I haven't had much time to play but have seen it with a stock kernel at least as far back as v5.0. They all triple-fault on bringing up secondary CPUs, on kexec.

-- 
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