linux-kernel - Re: [PATCH 0/3] Infinite loops in microcode while running guests

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Date:	Wed, 11 Nov 2015 07:47:50 -0500
From:	Austin S Hemmelgarn <ahferroin7@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc:	digitaleric@...gle.com
Subject: Re: [PATCH 0/3] Infinite loops in microcode while running guests

On 2015-11-10 07:22, Paolo Bonzini wrote:
> Yes, these can happen.  The issue is that benign exceptions are
> delivered serially, but two of them (#DB and #AC) can also happen
> during exception delivery itself.  The subsequent infinite stream
> of exceptions causes the processor to never exit guest mode.
>
> Paolo
>
> Eric Northup (1):
>    KVM: x86: work around infinite loop in microcode when #AC is delivered
>
> Paolo Bonzini (2):
>    KVM: svm: unconditionally intercept #DB
>    KVM: x86: rename update_db_bp_intercept to update_bp_intercept
>
>   arch/x86/include/asm/kvm_host.h |  2 +-
>   arch/x86/include/uapi/asm/svm.h |  1 +
>   arch/x86/kvm/svm.c              | 22 +++++++++++-----------
>   arch/x86/kvm/vmx.c              |  7 +++++--
>   arch/x86/kvm/x86.c              |  2 +-
>   5 files changed, 19 insertions(+), 15 deletions(-)
>
I just finished running a couple of tests in a KVM instance running 
nested on a Xen HVM instance, and found no issues, so for the set as a 
whole:

Tested-by: Austin S. Hemmelgarn <ahferroin7@...il.com>

Now to hope the equivalent fix for Xen gets into the Gentoo repositories 
soon, as the issue propagates down through nested virtualization and 
ties up the CPU regardless (and in turn triggers the watchdog).


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