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Re: [Xen-devel] [PATCH 2/5] x86/idle: re-arrange dead-idle handling
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 5 Dec 2018 20:33:47 +0000
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- Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 05 Dec 2018 20:34:10 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 10/09/2018 11:13, Jan Beulich wrote:
>
>> Equally, it may still be able to service #MC's, so I can't see how it is
>> safe for us to ever free the percpu data.
> I'm having trouble seeing how this remark relates to the series here.
Because you've tried to make NMIs safe, but not made equivalent
adjustments to the #MC side of things.
> Plus it's a theoretical problem at present only anyway:
> - physical hot remove is not implemented (there's no source of the
> new CPU_REMOVE notification),
> - Intel CPUs get parked, i.e. never have their per-CPU data freed,
> - AMD CPUs don't broadcast #MC.
Ignoring MCE's is never an option, but whenever CR4.MCE is set, we must
be prepared to handle #MC. Just because an AMD CPU is playing dead
doesn't mean it is immune to receiving #MC's.
~Andrew
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