From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH 0/2] KVM guest-kernel panics double fault
Date: Mon, 16 Jan 2012 07:58:09 -0200
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Cc: Jan Kiszka <jan.kiszka@siemens.com>, kvm@vger.kernel.org
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On Sun, Jan 15, 2012 at 08:44:50PM +0100, Stephan B=E4rwolf wrote:
> Thank you for applying this, Marcelo.
>=20
> I fear we (or me after I agreed) did some mistake by erasing the addi=
tional
> cpuid 0x80000001 checks.
> In contradiction to only AMD it MUST also apply on Intel-CPUs.
>=20
> Documentation
> "http://www.intel.com/content/dam/doc/manual/64-ia-32-architectures-s=
oftware-developer-manual-325462.pdf"
> Vol. 2A 3-207 (PDF-page 811) first block of table.
> (in addition AMD's doku "http://support.amd.com/us/Processor_TechDocs=
/APM_V3_24594.pdf"
> page 376 (PDF-page 408) table "Exceptions" on the bottom)
>=20
> Not all CPUs might have a syscall op at all (even in longmode) - they=
 informing about that
> via cpuid (But MSR_EFER may be still set).
> (You can force it externally in qemu-kvm-emulation via "-cpu host,-sy=
scall" ...)
> So an (guest) operating-system might not install *STAR-registers and =
crash again on such vcpus, right?

No because if the operating system does not install the STAR MSRs, it
will not set SCE bit in MSR_EFER (and your patch handles that=20
situation).