linux-kernel - Re: [PATCH] x86/asm/entry/64: better check for canonical address

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Message-ID: <20150327113430.GC14778@gmail.com>
Date:	Fri, 27 Mar 2015 12:34:30 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Brian Gerst <brgerst@...il.com>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/asm/entry/64: better check for canonical address


* Brian Gerst <brgerst@...il.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
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