linux-kernel - RE: [PATCH] x86/mce/AMD: Fix partial SMCA bank init when CPU 0 != thread 0

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Date:   Wed, 28 Jun 2017 18:58:36 +0000
From:   "Ghannam, Yazen" <Yazen.Ghannam@....com>
To:     Jack Miller <jack@...ezen.org>
CC:     Borislav Petkov <bp@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCH] x86/mce/AMD: Fix partial SMCA bank init when CPU 0 !=
 thread 0

> -----Original Message-----
> From: themoken@...il.com [mailto:themoken@...il.com] On Behalf Of
> Jack Miller
> Sent: Wednesday, June 28, 2017 2:53 PM
> To: Ghannam, Yazen <Yazen.Ghannam@....com>
> Cc: Jack Miller <jack@...ezen.org>; Borislav Petkov <bp@...e.de>; linux-
> kernel@...r.kernel.org; tglx@...utronix.de; x86@...nel.org
> Subject: Re: [PATCH] x86/mce/AMD: Fix partial SMCA bank init when CPU 0 !=
> thread 0
> 
> On Wed, Jun 28, 2017 at 1:00 PM, Ghannam, Yazen
> <Yazen.Ghannam@....com> wrote:
> >> -----Original Message-----
> >> From: themoken@...il.com [mailto:themoken@...il.com] On Behalf Of
> >> Jack Miller
> >> Sent: Wednesday, June 28, 2017 1:44 PM
> >> To: Borislav Petkov <bp@...e.de>
> >> Cc: Jack Miller <jack@...ezen.org>; linux-kernel@...r.kernel.org;
> >> tglx@...utronix.de; Ghannam, Yazen <Yazen.Ghannam@....com>;
> >> x86@...nel.org
> >> Subject: Re: [PATCH] x86/mce/AMD: Fix partial SMCA bank init when CPU
> >> 0 != thread 0
> >>
> >> On Wed, Jun 28, 2017 at 4:22 AM, Borislav Petkov <bp@...e.de> wrote:
> >> > On Tue, Jun 27, 2017 at 07:06:30PM -0500, Jack Miller wrote:
> >> >> After a call to firmware SwitchBSP(),
> >> >
> >> > What is that and who does that?
> >>
> >> SwitchBSP() is part of the UEFI MPServices Protocol which I believe
> >> is an extension but it is supported by all of the firmwares I've tested on.
> >>
> >> In this case, I'm using a bootloader to SwitchBSP() so that hardware
> >> thread 0 (and thus core 0) can be offlined on AMD hardware
> >> (cpu0_hotplug unsupported). This is currently working by passing
> >> 'nomce' to the kernel, but obviously I'd prefer not to disable it.
> >>
> >
> > Which core are you using as the BSP with SwitchBSP()?
> 
> Core 4, hardware thread 8 overall. I am testing on a Ryzen 7 machine.
> 
> >
> >> >
> >> >> Linux can be booted with a thread
> >> >> that isn't the first in the system. That thread automatically
> >> >> becomes CPU 0.
> >> >
> >> > Btw, you should be seeing other explosions too as a lot of code
> >> > assumes CPU 0 is the BSP.
> >>
> >> Actually, with 'nomce' or this patch applied the system seems to chug
> >> along merrily, no further errors in dmesg, no further BUGs. Linux
> >> still gets all of the topology correct (i.e. CPU 0's
> >> core/thread/siblings are correctly identified) so really, aside from
> >> userspace programs doing naive stuff with CPU affinity (like
> >> expecting even,odd CPUs to be SMT pairs), I think the overall result
> >> here is that most threads are interchangeable... except when probing
> certain features like these MCA types.
> >>
> >
> > Do you see 23 banks named in the new BSP's
> > /sys/devices/system/machinecheck/ folder? You should see non-core banks
> like l3_cache, umc, etc.
> 
> With my patch applied, I see entries like l3_cache under hardware thread 0's
> directory (it's shifted to CPU 1, so machinecheck1).
> Without my patch, only machinecheck0 has anything interesting in it
> (insn_fetch, l2_cache etc.) because the init failed on CPU 1.
> 

What happens with SMT off?

Thanks,
Yazen