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Re: [PATCH v2] x86/intel: workaround several MONITOR/MWAIT errata
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Alejandro Vallejo <agarciav@xxxxxxx>
- Date: Fri, 25 Apr 2025 13:36:42 +0100
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Frediano Ziglio <frediano.ziglio@xxxxxxxxx>, Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 25 Apr 2025 12:37:02 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Wed Apr 23, 2025 at 12:32 PM BST, Roger Pau Monne wrote:
> There are several errata on Intel regarding the usage of the MONITOR/MWAIT
> instructions, all having in common that stores to the monitored region
> might not wake up the CPU.
>
> Fix them by forcing the sending of an IPI for the affected models.
>
> The Ice Lake issue has been reproduced internally on XenServer hardware,
> and the fix does seem to prevent it. The symptom was APs getting stuck in
> the idle loop immediately after bring up, which in turn prevented the BSP
> from making progress.
Ugh... so this is what it was... Awesome having this madness fixed.
Do you happen to know if Linux has a similar fix in place?
> This would happen before the watchdog was initialized, and hence the
> whole system would get stuck.
That's nasty. It was the misassumption that the watchdog was already
running that had me going in circles thinking it was a lockup rather
than a livelock. Oh, well.
I believe the kudos for finally being able to reproduce this goes to
Frediano?
Cheers,
Alejandro
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