linux-kernel - Re: [PATCH] KVM: x86: expose MSR_TSC

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Message-ID: <253597133.12158605.1447407774121.JavaMail.zimbra@redhat.com>
Date:	Fri, 13 Nov 2015 04:42:54 -0500 (EST)
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Peter Hornyack <peterhornyack@...gle.com>
Cc:	kvm list <kvm@...r.kernel.org>, linux-kernel@...r.kernel.org,
	Radim Krcmar <rkrcmar@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: expose MSR_TSC_AUX to userspace


> Paolo, under what circumstances (which versions of Windows? Anything
> special running in the guest?) has this failure happened? I'd like to repro
> this, I'm not sure if we've observed it before.

We saw it with migration under Windows 10, nothing special running in the
guest.  It's very hard to reproduce, we've only seen it once but the BSOD
parameters provided surprisingly good evidence:

----------------------------------
CRITICAL_STRUCTURE_CORRUPTION (109)
This bugcheck is generated when the kernel detects that critical kernel code or
data have been corrupted. There are generally three causes for a corruption:
1) A driver has inadvertently or deliberately modified critical kernel code
 or data. See http://www.microsoft.com/whdc/driver/kernel/64bitPatching.mspx
2) A developer attempted to set a normal kernel breakpoint using a kernel
 debugger that was not attached when the system was booted. Normal breakpoints,
 "bp", can only be set if the debugger is attached at boot time. Hardware
 breakpoints, "ba", can be set at any time.
3) A hardware corruption occurred, e.g. failing RAM holding kernel code or data.
Arguments:
Arg1: a3a01f58a88e3638, Reserved
Arg2: b3b72bdefb0f076f, Reserved
Arg3: 00000001c0000103, Failure type dependent information
Arg4: 0000000000000007, Type of corrupted region, can be
	...
	7   : Critical MSR modification
----------------------------------

Argument 1 and 2 might be related to the old and new value (perhaps some
kind of hash).

Argument 3 is not documented either, but the low 32 bits look a lot like
the MSR_TSC_AUX index. :)

Paolo
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