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

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Message-ID: <20140422112312.GB15882@pd.tnic>
Date:	Tue, 22 Apr 2014 13:23:12 +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 Mon, Apr 21, 2014 at 06:53:36PM -0700, Andrew Lutomirski wrote:
> On Mon, Apr 21, 2014 at 6:47 PM, H. Peter Anvin <hpa@...or.com> wrote:
> > Race condition (although with x86 being globally ordered, it probably can't actually happen.) The bitmask is probably the way to go.
> 
> Does the race matter?  In the worst case you take the lock
> unnecessarily.  But yes, the bitmask is easy.

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 :-)

-- 
Regards/Gruss,
    Boris.

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