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

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Date:   Wed, 3 Jan 2018 14:03:50 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Jia Zhang <qianyue.zj@...baba-inc.com>, mingo@...hat.com,
        hpa@...or.com, tglx@...utronix.de, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] x86/microcode/intel: Blacklist the specific BDW-EP
 for late loading

On Tue, Jan 02, 2018 at 11:24:18AM -0800, Luck, Tony wrote:
> Should there be a "Cc: stable ..." in there?
> 
> The original patch that disables for all broadwell
> seems to be geting applied to a bunch of older trees,
> I think we want this one to chase after it.
> 
> Perhaps a
> 
> Fixes: 723f2828a98c ("x86/microcode/intel: Disable late loading on model 79")
> 
> too?

Done and done.

Thx!

---
From: Jia Zhang <qianyue.zj@...baba-inc.com>
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@...baba-inc.com>
Acked-by: Tony Luck <tony.luck@...el.com>
Cc: x86-ml <x86@...nel.org>
Cc: <stable@...r.kernel.org> # v4.14
Fixes: 723f2828a98c ("x86/microcode/intel: Disable late loading on model 79")
Link: http://lkml.kernel.org/r/1514772287-92959-1-git-send-email-qianyue.zj@alibaba-inc.com
[ Heavily massage commit message and pr_* statements. ]
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 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.

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