linux-kernel - Re: [patch 0/6] Cure kexec() vs. mwait_play

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Date:   Fri, 16 Jun 2023 12:00:13 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Ashok Raj <ashok.raj@...el.com>
Cc:     Ashok Raj <ashok_raj@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Ashok Raj <ashok.raj@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Vijay Dhanraj <vijay.dhanraj@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Laszlo Ersek <lersek@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Andrea Bolognani <abologna@...hat.com>,
        "Daniel P. Berrangé" <berrange@...hat.com>
Subject: Re: [patch 0/6] Cure kexec() vs. mwait_play_dead() troubles

On Fri, Jun 16, 2023, Ashok Raj wrote:
> On Wed, Jun 07, 2023 at 08:46:22PM -0700, Sean Christopherson wrote:
> > 
> > https://lore.kernel.org/all/BYAPR12MB301441A16CE6CFFE17147888A0A09@BYAPR12MB3014.namprd12.prod.outlook.com
> > 
> > > If there is a specific test you want done, let me know.
> > 
> > Smoke testing is all I was thinking.  I wouldn't put too much effort into trying
> > to make sure this all works.  Like I said earlier, nice to have, but certainly not
> > necessary.
> 
> + Vijay who was helping with testing this inside the VM.
> + Paolo, Laszlo 
> 
> I haven't found the exact method to test with secure boot/trusted boot yet.
> But here is what we were able to test thus far.
> 
> Vijay was able to get OVMF recompiled with SMM included.
> 
> Thanks to Laszlo for pointing me in the right direction. And Paolo for
> helping with some basic questions.
> 
> https://github.com/tianocore/tianocore.github.io/wiki/Testing-SMM-with-QEMU,-KVM-and-libvirt
> 
> Surprisingly SMM emulation is sadly damn good :-) 
> 
> Recipe is to generate SMI by writing to port 0xb2. 
> 
> - On native, this does generate a broadcast SMI, the SMI_COUNT MSR 0x34
>   goes up by 1 on all logical CPUs.
> - Turn off SMT by #echo off > /sys/devices/system/cpu/smt/control
> - Do another port 0xb2, we don't see any hangs
> - Bring up SMT by echo on > control, and we can see even the offline CPUs
>   got the SMI as indicated by MSR 0x34. (Which is as expected)
> 
> On guest, the only difference was when we turn on HT again, waking the CPUs
> from INIT, SMI_COUNT has zeroed as opposed to the native. (Which is
> perfectly fine) All I was looking for was "no hang". And a normal kexec
> with newly updated code works well inside a guest.
> 
> Would this qualify for the smoke test pass? I'll continue to look for a
> secure boot install if this doesn't close it, just haven't landed at the
> right spot yet.

Good enough for me, thanks much!