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Date: Mon, 5 Aug 2013 20:43:02 +0300
From: Gleb Natapov <gleb@redhat.com>
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Subject: Re: [Qemu-devel] [Bug 1208540] [NEW] RDMSR of register 0x345
 (IA32_PERF_CAPABILITIES)	fails in guest
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To: Bug 1208540 <1208540@bugs.launchpad.net>
Cc: qemu-devel@nongnu.org

On Mon, Aug 05, 2013 at 05:17:30PM -0000, Jari Ruusu wrote:
> Public bug reported:
> 
> I have a problem with qemu when I attempt to configure qemu in a way that
> AES-NI op-codes are enabled in quest. To do that, I have to configure qemu
> to emulate a recent CPU. But that causes a problem, because with recent
> CPUs, guest linux kernel code assumes that RDMSR of register 0x345 works.
> Qemu does not handle that correctly. Qemu does not crash. Guests running
> newer linux kernels always crash on boot with 'general protection fault' on
> RDMSR op-code that attempts to read IA32_PERF_CAPABILITIES. That "crashing"
> linux code works OK on bare metal.
> 
This is not QEMU/KVM bug, this is kernel bug since it should not touch
this MSR if cpuid does not have PDCM bit. Compile your guest kernel with
paravirt support (which is a good idea for many reasons) and the crash
will disappear.

--
			Gleb.