linux-kernel - Re: [PATCH 4/8] x86: Add support for rd/wr fs/gs base

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Message-ID: <20150410205702.GV15335@tassilo.jf.intel.com>
Date:	Fri, 10 Apr 2015 13:57:02 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andi Kleen <andi@...stfloor.org>, X86 ML <x86@...nel.org>,
	Andrew Lutomirski <luto@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 4/8] x86: Add support for rd/wr fs/gs base

> I think all of this stems from unfortunate naming.  DEBUG_STACK isn't
> one stack -- it's a debug stack *array*.  The IST shift mechanism
> means that we can use different entries in that array as our stacks
> depending on how deeply nested we are.

I still think it's a terrible idea.

> > Just handling it in the code is simple enough.
> 
> It seems to account for over half the asm diff.  I'm talking about the
> addition of approximately two lines of C and the removal of a huge
> chunk of the asm diff.

It's just adding offsets to the stack code. Nothing complicated.
It's also straight forward code. Far more preferable than your magic
overlapping stacks.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only
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