Re: [Xen-devel] [PATCH v5] x86/AMD: Add support for AMD's OSVW feature in guests

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On 02/06/12 19:44, Boris Ostrovsky wrote:
> On 02/06/12 12:47, Konrad Rzeszutek Wilk wrote:
> > On Mon, Feb 06, 2012 at 06:39:25PM +0100, Boris Ostrovsky wrote:
> > > # HG changeset patch
> > > # User Boris Ostrovsky<boris.ostrovsky@xxxxxxx>
> > > # Date 1328549858 -3600
> > > # Node ID 3cf8ffd0ab883dd09f943f4d8fb50f5cc1f04cd5
> > > # Parent e2722b24dc0962de37215320b05d1bb7c4c42864
> > > x86/AMD: Add support for AMD's OSVW feature in guests.
> > >
> > > In some cases guests should not provide workarounds for errata even
> > > when the
> > > physical processor is affected. For example, because of erratum 400
> > > on family
> > > 10h processors a Linux guest will read an MSR (resulting in VMEXIT)
> > > before
> > > going to idle in order to avoid getting stuck in a non-C0 state. This
> > > is not
> > What about fixing the Linux guest to actually not do this? I presume you
> > have encountered this with HVM guests - would it be possible to use
> >
> > set_pm_idle_to_default(default_idle) in the HVM bootup path, say in
> > 'xen_hvm_guest_init' ??
>
> Changing Linux won't help guests running Linux prior to the change so we
> still need this patch. And with the patch guest's pm_idle will be set to
> default_idle anyway (because cpu_has_amd_erratum(amd_erratum_400) will
> return 0).
Right. Also fixing Linux won't help non-Linux guests, too.

Christoph


> -boris
>
> > > necessary: HLT and IO instructions are intercepted and therefore
> > > there is no
> > > reason for erratum 400 workaround in the guest.
> > >
> > > This patch allows us to present a guest with certain errata as fixed,
> > > regardless of the state of actual hardware.

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