Re: [PATCH v2 for-4.15] x86/msr: introduce an option for HVM relaxed rdmsr behavior

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 3/4/21 9:47 AM, Roger Pau Monne wrote:
> Introduce an option to allow selecting a less strict behaviour for
> rdmsr accesses targeting a MSR not explicitly handled by Xen. Since
> commit 84e848fd7a162f669 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 commit attempts to offer a fallback option similar to the
> previous behavior. Note however that the value of the underlying MSR
> is never leaked to the guest, as the newly introduced option only
> changes whether a #GP is injected or not.
>
> Long term the plan is to properly handle all the MSRs, so the option
> introduced here should be considered a temporary resort for OSes that
> don't work properly with the new MSR policy. Any OS that requires this
> option to be enabled should be reported to
> xen-devel@lists.xenproject.org.
>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> Changes since v1:
>  - Only apply the option to HVM guests.
>  - Only apply the special handling to MSR reads.
>  - Sanitize the newly introduced flags field.
>  - Print a warning message when the option is used.
> ---
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> ---
> Boris, could you please test with Solaris to see if this fixes the
> issue?


Yes, still works. (It worked especially well after I noticed new option name ;-))


-boris