linux-kernel - Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

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Message-ID: <4E678992.5050709@redhat.com>
Date:	Wed, 07 Sep 2011 18:11:14 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Don Zickus <dzickus@...hat.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM <kvm@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
Subject: Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

On 09/07/2011 04:44 PM, Don Zickus wrote:
> >
> >  Is there a way to tell whether an NMI was internally or externally
> >  generated?
> >
> >  I don't think so, especially as two or more NMIs can be coalesced.
> >  So any NMI received on this first cpu has to check the NMI reason
> >  port?
>
> Well we cheat and execute all the nmi handlers first.  If they come back
> as handled, we skip the check for the external NMI.

And hope that no other NMI was generated while we're handling this one.  
It's a little... fragile?

> But you are right, other than checking the reason port, there isn't a way
> to determine if an NMI is internally or externally generated.

Ouch.

>
> >
> >  >>
> >  >>   But on the other hand, I don't really care if you can say that this path
> >  >>   will never be called in a virtual machine.
> >  >
> >  >Does virtual machines support hot remove of cpus?  Probably not
> >  >considering bare-metal barely supports it.
> >  >
> >
> >  They do.
>
> But vcpus probably don't have the notion of a bsp cpu, so perhaps virtual
> machines can get away with it easier?  (I don't know enough about the hot
> cpu remove code to really explain it, just enough to know it can cause
> problems and people are trying to address it).
>

The concept of a bsp exists in exactly the same way as on real hardware.

-- 
error compiling committee.c: too many arguments to function

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