linux-kernel - [tip:x86/cache] x86/intel_rdt: Turn off most RDT features on Skylake

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Date:   Fri, 25 Aug 2017 13:04:48 -0700
From:   tip-bot for Tony Luck <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, davidcc@...gle.com, vikas.shivappa@...ux.intel.com,
        ak@...ux.intel.com, eranian@...gle.com, tony.luck@...el.com,
        fenghua.yu@...el.com, peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, ravi.v.shankar@...el.com,
        tglx@...utronix.de
Subject: [tip:x86/cache] x86/intel_rdt: Turn off most RDT features on
 Skylake

Commit-ID:  d56593eb5eda8f593db92927059697bbf89bc4b3
Gitweb:     http://git.kernel.org/tip/d56593eb5eda8f593db92927059697bbf89bc4b3
Author:     Tony Luck <tony.luck@...el.com>
AuthorDate: Thu, 24 Aug 2017 09:26:52 -0700
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 25 Aug 2017 22:00:45 +0200

x86/intel_rdt: Turn off most RDT features on Skylake

Errata list is included in this document:
https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/6th-gen-x-series-spec-update.pdf
with more details in:
https://www.intel.com/content/www/us/en/processors/xeon/scalable/xeon-scalable-spec-update.html

But the tl;dr summary (using tags from first of the documents) is:
SKZ4  MBM does not accurately track write bandwidth
SKZ17 CMT counters may not count accurately
SKZ18 CAT may not restrict cacheline allocation under certain conditions
SKZ19 MBM counters may undercount

Disable all these features on Skylake models. Users who understand the
errata may re-enable using boot command line options.

Signed-off-by: Tony Luck <tony.luck@...el.com>
Cc: Fenghua" <fenghua.yu@...el.com>
Cc: Ravi V" <ravi.v.shankar@...el.com>
Cc: "Peter Zijlstra" <peterz@...radead.org>
Cc: "Stephane Eranian" <eranian@...gle.com>
Cc: "Andi Kleen" <ak@...ux.intel.com>
Cc: "David Carrillo-Cisneros" <davidcc@...gle.com>
Cc: Vikas Shivappa <vikas.shivappa@...ux.intel.com>
Link: http://lkml.kernel.org/r/3aea0a3bae219062c812668bd9b7b8f1a25003ba.1503512900.git.tony.luck@intel.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 arch/x86/kernel/cpu/intel_rdt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
index b641622..cd5fc61 100644
--- a/arch/x86/kernel/cpu/intel_rdt.c
+++ b/arch/x86/kernel/cpu/intel_rdt.c
@@ -769,6 +769,9 @@ static __init void rdt_quirks(void)
 		if (!rdt_options[RDT_FLAG_L3_CAT].force_off)
 			cache_alloc_hsw_probe();
 		break;
+	case INTEL_FAM6_SKYLAKE_X:
+		if (boot_cpu_data.x86_mask <= 4)
+			set_rdt_options("!cmt,!mbmtotal,!mbmlocal,!l3cat");
 	}
 }