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Message-ID: <3908561D78D1C84285E8C5FCA982C28F3292BD44@ORSMSX114.amr.corp.intel.com>
Date: Thu, 13 Nov 2014 00:31:30 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: Andy Lutomirski <luto@...capital.net>
CC: Oleg Nesterov <oleg@...hat.com>, Borislav Petkov <bp@...en8.de>,
X86 ML <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
"Andi Kleen" <andi@...stfloor.org>
Subject: RE: [RFC PATCH] x86, entry: Switch stacks on a paranoid entry from
userspace
> v2's not going to make a difference unless you're using uprobes at the
> same time.
Not (knowingly) using uprobes. System is installed with a RHEL7 userspace ... but is essentially
idle except for my test program.
> In the interest of my sanity, can you add something like
> BUG_ON(!user_mode_vm(regs)) or the mce_panic equivalent before calling
> memory_failure?
I don't think that can possibly trip - we can only end up with a recoverable error from
a user mode access. But I'll see about adding it anyway
> What happens if there's a shared bank but the actual offender has a
> higher order than the cpu that finds the error?
This test case injects a memory error which is logged in bank1. This bank is shared by the
two hyperthreads that are on the same core. The mce_severity() function distinguishes
which is the active thread and which the innocent bystander by looking at MCG_STATUS.
In the active thread MCG_STATUS.EIPV is 1, in the bystander it is 0. The returned severity
is MCE_AR_SEVERITY for the thread that hit the error, MCE_KEEP_SEVERITY for the bystander.
So it doesn't matter which thread has the lower order and sees it first.
> Is this something I can try under KVM?
I don't know if KVM has a way to simulate a machine check event.
-Tony
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