linux-kernel - Re: [RFC/HACK] x86: Fast return to kernel

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Message-ID: <536411C1.4040209@intel.com>
Date:	Fri, 02 May 2014 14:44:33 -0700
From:	"H. Peter Anvin" <h.peter.anvin@...el.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC/HACK] x86: Fast return to kernel

On 05/02/2014 02:42 PM, Andy Lutomirski wrote:
> 
> Hah -- I think I just faked both of you out :)
> 
> I don't think this has anything to do with the error code, and I think
> that the errorentry code already does more or less that: it pushes -1.
> 
> The real issue here is probably the magic 16-byte stack alignment when
> a non-stack-switching interrupt happens.
> 

Errorentry is when there *is* an error code pushed by the hardware.  The
other variant is zeroentry, which does generate a zero error code --
eventually.  The -1 means we didn't enter the kernel through a system call.

	-hpa

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