linux-kernel - Re: [PATCH v2 1/2] x86/AMD: Fix cpu_llc

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Date:   Fri, 28 Oct 2016 18:57:40 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Yazen Ghannam <Yazen.Ghannam@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems

On Fri, Oct 28, 2016 at 10:51:57AM -0500, Yazen Ghannam wrote:
> The current Fam17h cpu_llc_id  derivation has an underflow bug when
				^
			(Last Level Cache ID)

Let's write it out the first time.

> extracting the socket_id value. The socket_id value starts from 0, so
> subtracting 1 will result in an underflow. This breaks scheduling topology
> later on since the cpu_llc_id will be incorrect.
> 
> The apicid decoding is fixed for bits 3 and above,
						    ^
"is fixed ... in register... "

> which give the core
> complex, node and socket IDs. The LLC is at the core complex level so we
> can find a unique cpu_llc_id by right shifting the apicid by 3.

"... because then the LSBit will be the Core Complex ID."

> We can fix the underflow bug and simplify the code by replacing the
> current cpu_llc_id derivation with a right shift.
> 
> Signed-off-by: Yazen Ghannam <Yazen.Ghannam@....com>
> Cc: <stable@...r.kernel.org> # v4.4..
> Fixes: 3849e91f571d ("x86/AMD: Fix last level cache topology for AMD Fam17h systems")
> ---

I'll run it soon.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--