[PATCH v2] x86/microcode/intel: Extend BDW late-loading with LLC size check

[Jia Zhang]

The commit b94b73733171
("x86/microcode/intel: Extend BDW late-loading with a revision check")
reduces the impact of erratum BDF90 for Broadwell process model.
Actually, the impact can be reduced further through adding the checks
for the size of LLC per core.

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@xxxxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/microcode/intel.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index d9e460f..9143cf2 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -906,18 +906,29 @@ static int get_ucode_fw(void *to, const void *from, size_t n)
 	return 0;
 }
 
+static int 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;
+}
+
 static bool is_blacklisted(unsigned int cpu)
 {
 	struct cpuinfo_x86 *c = &cpu_data(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(c) > 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");
-- 
1.8.3.1