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

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Message-ID: <20150410204125.GS15335@tassilo.jf.intel.com>
Date:	Fri, 10 Apr 2015 13:41:25 -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

> It wouldn't take any additional memory at all.  Currently we have 8k
> of "debug" stack which is really two 4k pieces, and you're putting the
> kernel gs base in the bottom word.  I'm suggesting that you duplicate
> the kernel gs base at the bottom work and the bottom word + 4k.  We
> already have a hard limit of 4k of debug stack because of the IST
> shift mechanism -- it really is two separate 4k stacks, not one 8k
> stack.

Seems like a hack. What happens if we add an uneven number of stacks?

Just handling it in the code is simple enough.


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