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Re: [PATCH RFC for-4.15] x86/msr: introduce an option for legacy MSR behavior selection
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Mon, 1 Mar 2021 14:33:25 -0500
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- Cc: Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>
- Delivery-date: Mon, 01 Mar 2021 19:33:45 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 3/1/21 11:23 AM, Roger Pau Monne wrote:
> Introduce an option to allow selecting the legacy behavior for
> accesses to MSRs not explicitly handled. Since commit
> 84e848fd7a162f669 and 322ec7c89f6640e accesses to MSRs not explicitly
> handled by Xen result in the injection of a #GP to the guest. This is
> a behavior change since previously a #GP was only injected if
> accessing the MSR on the real hardware will also trigger a #GP.
>
> This seems to be problematic for some guests, so introduce an option
> to fallback to this legacy behavior. The main difference between what
> was previously done is that the hardware MSR value is not leaked to
> the guests on reads.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> ---
> Note that this option is not made available to dom0. I'm not sure
> whether it makes sense to do so, since anyone updating Xen to such
> newer version will also likely pair it with a newish kernel that
> doesn't require such workarounds.
>
> RFC because there's still some debate as to how we should solve the
> MSR issue, this is one possible way, but IMO we need to make a
> decision soon-ish because of the release timeline.
>
> Boris, could you please test with Solaris to see if this fixes the
> issue?
Yes, it does. Thanks.
-boris
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