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

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Message-ID: <20110726184744.GA8422@elte.hu>
Date:	Tue, 26 Jul 2011 20:47:44 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Borislav Petkov <bp@...64.org>
Cc:	Ray Lee <ray-lk@...rabbit.org>,
	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


* Borislav Petkov <bp@...64.org> wrote:

> > Was this done with a stock kernel, or with the simple patch 
> > applied?
> 
> with the simplest version of Linus' patch:
> 
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 1dab519..6b1094d 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -90,6 +90,8 @@ static unsigned long mmap_rnd(void)
>                         rnd = (long)get_random_int() % (1<<8);
>                 else
>                         rnd = (long)(get_random_int() % (1<<28));
> +
> +               rnd &= ~0x7;

So, unless i got the stats right, unmodified kernel has like a 75% 
mis-aligned rate, while with the simple fix this goes down to 30%?

Have you run the numbers on the stock, unmodified kernel by any 
chance, just to make sure the stats are ok?

Thanks,

	Ingo
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