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Subject: Re: [RFC][PATCH 3/3] x86: Add workaround to NMI iret woes
From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Jason Baron <jbaron@redhat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "H. Peter Anvin" <hpa@linux.intel.com>, Paul Turner <pjt@google.com>
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On Fri, 2011-12-09 at 16:10 +0100, Peter Zijlstra wrote:

> KVM does NMIs, the write_idt thing is a paravirt call. Then again, a
> vcpu is a single thread of execution, there can only ever be 1 hypercall
> at the same time.
> 
> The only thing that remains is if the hypercall interface is NMI-safe,
> what if the NMI comes in just as another context is also starting a
> hypercall. I really don't know enough about all that crap to know.

Hmm, well we can detect that we are a paravirt guest or not (that's the
nature of paravirt). We can keep the current methods around, an for
paravirt guests, it will fall back to the old stop_machine() method.
Heck guests have issues with latencies anyway.

For running on bare-metal, we can switch to this method.

-- Steve