linux-kernel - [PATCH 4.4 01/31] x86/cpu/AMD: Fix cpu_llc

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Date:   Thu, 24 Nov 2016 15:55:22 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        Yazen Ghannam <Yazen.Ghannam@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Aravind Gopalakrishnan <aravindksg.lkml@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.4 01/31] x86/cpu/AMD: Fix cpu_llc_id for AMD Fam17h systems

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yazen Ghannam <Yazen.Ghannam@....com>

commit b0b6e86846093c5f8820386bc01515f857dd8faa upstream.

cpu_llc_id (Last Level Cache ID) derivation on AMD Fam17h has an
underflow bug when extracting the socket_id value. It starts from 0
so subtracting 1 from it will result in an invalid value. This breaks
scheduling topology later on since the cpu_llc_id will be incorrect.

For example, the the cpu_llc_id of the *other* CPU in the loops in
set_cpu_sibling_map() underflows and we're generating the funniest
thread_siblings masks and then when I run 8 threads of nbench, they get
spread around the LLC domains in a very strange pattern which doesn't
give you the normal scheduling spread one would expect for performance.

Other things like EDAC use cpu_llc_id so they will be b0rked too.

So, the APIC ID is preset in APICx020 for bits 3 and above: they contain
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 least significant bit
will be the Core Complex ID.

Tested-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Yazen Ghannam <Yazen.Ghannam@....com>
[ Cleaned up and extended the commit message. ]
Signed-off-by: Borislav Petkov <bp@...e.de>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Aravind Gopalakrishnan <aravindksg.lkml@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Fixes: 3849e91f571d ("x86/AMD: Fix last level cache topology for AMD Fam17h systems")
Link: http://lkml.kernel.org/r/20161108083506.rvqb5h4chrcptj7d@pd.tnic
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/cpu/amd.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -352,7 +352,6 @@ static void amd_detect_cmp(struct cpuinf
 #ifdef CONFIG_SMP
 	unsigned bits;
 	int cpu = smp_processor_id();
-	unsigned int socket_id, core_complex_id;

 	bits = c->x86_coreid_bits;
 	/* Low order bits define the core id (index of core in socket) */
@@ -370,10 +369,7 @@ static void amd_detect_cmp(struct cpuinf
 	 if (c->x86 != 0x17 || !cpuid_edx(0x80000006))
 		return;

-	socket_id	= (c->apicid >> bits) - 1;
-	core_complex_id	= (c->apicid & ((1 << bits) - 1)) >> 3;
-
-	per_cpu(cpu_llc_id, cpu) = (socket_id << 3) | core_complex_id;
+	per_cpu(cpu_llc_id, cpu) = c->apicid >> 3;
 #endif
 }