linux-kernel - Re: [PATCH] x86, AMD: Correct F15h IC aliasing issue

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Message-Id: <20110724091626.c6829ebe.akpm@linux-foundation.org>
Date:	Sun, 24 Jul 2011 09:16:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Borislav Petkov <bp@...64.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"Przywara, Andre" <Andre.Przywara@....com>,
	"Pohlack, Martin" <Martin.Pohlack@....com>
Subject: Re: [PATCH] x86, AMD: Correct F15h IC aliasing issue

On Sun, 24 Jul 2011 15:40:46 +0200 Borislav Petkov <bp@...64.org> wrote:

> > > +	unalias_va_addr
> > > +			[X86-64] Unalias VA address by clearing slice [14:12]
> > > +			1: only on 32-bit
> > > +			2: only on 64-bit
> > > +			off: disabled on both 32 and 64-bit

How much performance difference does this actually make?

> > This says nothing about why it's cleared, what it does and why one 
> > would want to handle it differently on 32-bit and 64-bit.
> 
> This is there in case users care more about the 3bits ASLR granularity
> than invalidations amount, for example.

To make this decision the users will want to know how much their
computers will slow down.  We should tell them.
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