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Date: Sun, 29 Mar 2015 10:51:22 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Hector Marco-Gisbert <hecmargi@upv.es>, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
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        kees Cook <keescook@chromium.org>,
        Ismael Ripoll <iripoll@disca.upv.es>
Subject: Re: [PATCH] mm/x86: AMD Bulldozer ASLR fix
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* Borislav Petkov <bp@alien8.de> wrote:

> From: Hector Marco-Gisbert <hecmargi@upv.es>
> Date: Fri, 27 Mar 2015 12:38:21 +0100
> Subject: [PATCH] x86/mm: Improve AMD Bulldozer ASLR fix
> 
> The ASLR implementation needs to special-case AMD F15h processors by
> clearing out bits [14:12] of the virtual address in order to avoid I$
> cross invalidations and thus performance penalty for certain workloads.
> For details, see:
> 
>   dfb09f9b7ab0 ("x86, amd: Avoid cache aliasing penalties on AMD family 15h")
> 
> This special case reduces the mmapped files entropy by eight.

s/reduces the mmapped file's entropy by 3 bits

Which does:

 - a grammar fix

 - measure it in bits, as later on we are talking about randomness in 
   bits as well.

Btw., does this limitation affect both executable and non-executable 
mmap()s? Because data mmap()s don't need this I$ related workaround, 
right? So we could relax it for data-mmap()s?

Thanks,

	Ingo