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

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)
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.



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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