linux-kernel - Re: [PATCH v3 4/4] x86/mce: Add Zhaoxin LMCE support

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Date:   Tue, 17 Sep 2019 09:37:05 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Tony W Wang-oc <TonyWWang-oc@...oxin.com>
Cc:     "Borislav Petkov (bp@...en8.de)" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yazen.ghannam@....com" <yazen.ghannam@....com>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
        "qiuxu.zhuo@...el.com" <qiuxu.zhuo@...el.com>,
        David Wang <DavidWang@...oxin.com>,
        "Cooper Yan(BJ-RD)" <CooperYan@...oxin.com>,
        "Qiyuan Wang(BJ-RD)" <QiyuanWang@...oxin.com>,
        "Herry Yang(BJ-RD)" <HerryYang@...oxin.com>
Subject: Re: [PATCH v3 4/4] x86/mce: Add Zhaoxin LMCE support

On Tue, Sep 17, 2019 at 06:54:05AM +0000, Tony W Wang-oc wrote:
> But have a question about below codes:
> 	if (mcgstatus & MCG_STATUS_RIPV) {
> 		mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
> 		return true;
> 	}
> These seems require all #MC exception errors set MCG_STATUS_RIPV = 1
> in order to skip synchronize which "return true;" actually does for this.
> 
> As Intel SDM show, "Recoverable-not-continuable SRAR Type" errors may
> set MCG_STATUS_RIPV = 0, PCC = 0. When these #MC errors broadcast
> to offline CPU, may cause kernel panic with synchronize timeout (offline
> CPU can't skip synchronize in this case).
> 
> Could "return true;" outside the if-case?
> 	if (mcgstatus & MCG_STATUS_RIPV) {
> 		mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
> 	} 
> 	return true; 

If RIPV bit is not set in mcgstatus, then where will the CPU return
to if you simply return from the #MC handler? RIPV=1 means that the
CPU pushed a valid return instruction pointer onto the stack.

E.g. in the not-continuable case you mention above? The CPU
will likely do something undefined if you try to continue a
not-continuable instruction.

-Tony