[PATCH 3.16 228/254] x86/microcode/intel: Extend BDW late-loading further with LLC size check

[Ben Hutchings]

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Jia Zhang <zhang.jia@xxxxxxxxxxxxxxxxx>

commit 7e702d17ed138cf4ae7c00e8c00681ed464587c7 upstream.

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.

Fixes: b94b73733171 ("x86/microcode/intel: Extend BDW late-loading with a revision check")
Signed-off-by: Jia Zhang <zhang.jia@xxxxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Tony Luck <tony.luck@xxxxxxxxx>
Link: https://lkml.kernel.org/r/1516321542-31161-1-git-send-email-zhang.jia@xxxxxxxxxxxxxxxxx
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/microcode/intel.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -87,6 +87,9 @@ MODULE_DESCRIPTION("Microcode Update Dri
 MODULE_AUTHOR("Tigran Aivazian <tigran@xxxxxxxxxxxxxxxxxxxx>");
 MODULE_LICENSE("GPL");
 
+/* last level cache size per core */
+static int llc_size_per_core;
+
 static int collect_cpu_info(int cpu_num, struct cpu_signature *csig)
 {
 	struct cpuinfo_x86 *c = &cpu_data(cpu_num);
@@ -273,12 +276,14 @@ static bool is_blacklisted(unsigned int
 
 	/*
 	 * 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 == 0x4F &&
 	    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");
@@ -345,6 +350,15 @@ static struct microcode_ops microcode_in
 	.microcode_fini_cpu               = microcode_fini_cpu,
 };
 
+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 = &cpu_data(0);
@@ -355,6 +369,8 @@ struct microcode_ops * __init init_intel
 		return NULL;
 	}
 
+	llc_size_per_core = calc_llc_size_per_core(c);
+
 	return &microcode_intel_ops;
 }