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Date: Fri, 27 Mar 2015 12:34:30 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
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Subject: Re: [PATCH] x86/asm/entry/64: better check for canonical address
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* Brian Gerst <brgerst@gmail.com> wrote:

> > Btw., there's a neat trick we could do: in the HLT, MWAIT and 
> > ACPI-idle code we could attempt to set up RCX to match RIP, to 
> > trigger this optimization in the common 'irq interrupted the idle 
> > task' case?
> 
> sysret only returns to CPL3.

Indeed, an IRET ought to be pretty cheap for same-ring interrupt 
returns in any case.

Thanks,

	Ingo