Re: [PATCH v5] x86/microcode/intel: Blacklist the specific BDW-EP for late loading

[Borislav Petkov]

On Mon, Jan 01, 2018 at 10:04:47AM +0800, Jia Zhang wrote:
> Instead of blacklisting all types of Broadwell processor when running
> a late loading, only BDW-EP (signature 0x406f1, aka family 6, model 79,
> stepping 1) with the microcode version less than 0x0b000021 needs to
> be blacklisted.
> 
> The erratum is documented in the the public documentation #334165 (See
> the item BDF90 for details).
> 
> Signed-off-by: Jia Zhang <qianyue.zj@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/microcode/intel.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)

Ok, I went and massaged your version, here's what I committed:

---
From: Jia Zhang <qianyue.zj@xxxxxxxxxxxxxxx>
Date: Mon, 1 Jan 2018 10:04:47 +0800
Subject: [PATCH] x86/microcode/intel: Extend BDW late-loading with a revision
 check

Instead of blacklisting all model 79 CPUs when attempting a late
microcode loading, limit that only to CPUs with microcode revisions <
0x0b000021 because only on those late loading may cause a system hang.

For such processors either:

a) a BIOS update which might contain a newer microcode revision

or

b) the early microcode loading method

should be considered.

Processors with revisions 0x0b000021 or higher will not experience such
hangs.

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 <qianyue.zj@xxxxxxxxxxxxxxx>
Acked-by: Tony Luck <tony.luck@xxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1514772287-92959-1-git-send-email-qianyue.zj@xxxxxxxxxxxxxxx
[ Heavily massage commit message and pr_* statements. ]
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/kernel/cpu/microcode/intel.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 8ccdca6d3f9e..d9e460fc7a3b 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -910,8 +910,17 @@ static bool is_blacklisted(unsigned int cpu)
 {
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
 
-	if (c->x86 == 6 && c->x86_model == INTEL_FAM6_BROADWELL_X) {
-		pr_err_once("late loading on model 79 is disabled.\n");
+	/*
+	 * 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).
+	 */
+	if (c->x86 == 6 &&
+	    c->x86_model == INTEL_FAM6_BROADWELL_X &&
+	    c->x86_mask == 0x01 &&
+	    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");
 		return true;
 	}
 
-- 
2.13.0

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.