linux-kernel - [PATCH 1/2] x86/microcode/intel: Extend BDW late-loading further with LLC size check

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Date:   Tue, 23 Jan 2018 11:41:32 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/2] x86/microcode/intel: Extend BDW late-loading further with LLC size check

From: Jia Zhang <zhang.jia@...ux.alibaba.com>

The commit

  b94b73733171 ("x86/microcode/intel: Extend BDW late-loading with a revision check")

reduced the impact of erratum BDF90 for Broadwell model 79.

The impact can be reduced further by checking the size of the last level
cache portion per core.

Tony: "The erratum says the problem only occurs on the large-cache SKUs.
So we only need to avoid the update if we are on a big cache SKU that is
also running old microcode."

For more details, see erratum BDF90 in document #334165 (Intel Xeon
Processor E7-8800/4800 v4 Product Family Specification Update) from
September 2017.

Signed-off-by: Jia Zhang <zhang.jia@...ux.alibaba.com>
Acked-by: Tony Luck <tony.luck@...el.com>
Cc: "hmh@....eng.br" <hmh@....eng.br>
Cc: x86-ml <x86@...nel.org>
Cc: <stable@...r.kernel.org> # v4.14
Link: http://lkml.kernel.org/r/1516321542-31161-1-git-send-email-zhang.jia@linux.alibaba.com
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/cpu/microcode/intel.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index d9e460fc7a3b..f7c55b0e753a 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -45,6 +45,9 @@ static const char ucode_path[] = "kernel/x86/microcode/GenuineIntel.bin";
 /* Current microcode patch used in early patching on the APs. */
 static struct microcode_intel *intel_ucode_patch;
 
+/* last level cache size per core */
+static int llc_size_per_core;
+
 static inline bool cpu_signatures_match(unsigned int s1, unsigned int p1,
 					unsigned int s2, unsigned int p2)
 {
@@ -912,12 +915,14 @@ static bool is_blacklisted(unsigned int cpu)
 
 	/*
 	 * Late loading on model 79 with microcode revision less than 0x0b000021
-	 * may result in a system hang. This behavior is documented in item
-	 * BDF90, #334165 (Intel Xeon Processor E7-8800/4800 v4 Product Family).
+	 * and LLC size per core bigger than 2.5MB may result in a system hang.
+	 * This behavior is documented in item BDF90, #334165 (Intel Xeon
+	 * Processor E7-8800/4800 v4 Product Family).
 	 */
 	if (c->x86 == 6 &&
 	    c->x86_model == INTEL_FAM6_BROADWELL_X &&
 	    c->x86_mask == 0x01 &&
+	    llc_size_per_core > 2621440 &&
 	    c->microcode < 0x0b000021) {
 		pr_err_once("Erratum BDF90: late loading with revision < 0x0b000021 (0x%x) disabled.\n", c->microcode);
 		pr_err_once("Please consider either early loading through initrd/built-in or a potential BIOS update.\n");
@@ -975,6 +980,15 @@ static struct microcode_ops microcode_intel_ops = {
 	.apply_microcode                  = apply_microcode_intel,
 };
 
+static int __init calc_llc_size_per_core(struct cpuinfo_x86 *c)
+{
+	u64 llc_size = c->x86_cache_size * 1024;
+
+	do_div(llc_size, c->x86_max_cores);
+
+	return (int)llc_size;
+}
+
 struct microcode_ops * __init init_intel_microcode(void)
 {
 	struct cpuinfo_x86 *c = &boot_cpu_data;
@@ -985,5 +999,7 @@ struct microcode_ops * __init init_intel_microcode(void)
 		return NULL;
 	}
 
+	llc_size_per_core = calc_llc_size_per_core(c);
+
 	return &microcode_intel_ops;
 }
-- 
2.13.0