RE: [PATCH v3 1/2] x86: mce: kexec: switch MCE handler for kexec/kdump

From: "Luck, Tony" <tony.luck@intel.com>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	Borislav Petkov <bp@alien8.de>
Cc: Prarit Bhargava <prarit@redhat.com>,
	Vivek Goyal <vgoyal@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Junichi Nomura <j-nomura@ce.jp.nec.com>,
	Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Subject: RE: [PATCH v3 1/2] x86: mce: kexec: switch MCE handler for kexec/kdump
Date: Tue, 3 Mar 2015 18:09:27 +0000	[thread overview]
Message-ID: <3908561D78D1C84285E8C5FCA982C28F329F5837@ORSMSX114.amr.corp.intel.com> (raw)
In-Reply-To: <1425373306-26187-1-git-send-email-n-horiguchi@ah.jp.nec.com>

+static void machine_check_under_kdump(struct pt_regs *regs, long error_code)
+{
+	if (mca_cfg.kdump_cpu == smp_processor_id())
+		pr_emerg("MCE triggered when kdumping. If you are lucky enough, you will have a kdump. Otherwise, this is a dying message.\n");

I'm worried about the SRAR case here.  Your code just returns, which will trigger the same machine check again. The system will spin forever printing this message.

I think you have to look at MCG_STATUS and scan the machine check banks to make a choice.  There are some simple cases:

  MCG_STATUS.RIPV=0 -> cannot return (where will the cpu go - you have no idea!)
  SRAO -> safe to just return
  SRAR -> should not return

But the rest may require some thought.  If there is a PCC=1 error, then you may end up with a corrupt dump. Perhaps this case will already be covered by RPIV==0?

-Tony