linux-kernel - Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

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Date:	Tue, 22 Apr 2014 16:46:59 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andrew Lutomirski <amluto@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Arjan van de Ven <arjan.van.de.ven@...el.com>,
	Brian Gerst <brgerst@...il.com>,
	Alexandre Julliard <julliard@...ehq.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

On Tue, Apr 22, 2014 at 01:23:12PM +0200, Borislav Petkov wrote:
> I wonder if it would be workable to use a bit in the espfix PGD to
> denote that it has been initialized already... I hear, near NX there's
> some room :-)

Ok, I realized this won't work when I hit send... Oh well.

Anyway, another dumb idea: have we considered making this lazy? I.e.,
preallocate pages to fit the stack of NR_CPUS after smp init is done but
not setup the percpu espfix stack. Only do that in espfix_fix_stack the
first time we land there and haven't been setup yet on this cpu.

This should cover the 1% out there who still use 16-bit segments and the
rest simply doesn't use it and get to save themselves the PT-walk in
start_secondary().

Hmmm...

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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