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Re: [PATCH v2 for-4.15] x86/msr: introduce an option for HVM relaxed rdmsr behavior
- To: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 4 Mar 2021 23:28:16 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 04/03/2021 23:09, Boris Ostrovsky wrote:
> 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@xxxxxxxxxxxxxxxxxxxx.
>>
>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> ---
>> 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@xxxxxxxxxx>
>> ---
>> 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
> ;-))
I'm afraid I want to break and rework how this bugfix happens. Solaris
is still broken on all older branches and this isn't a suitable fix to
backport.
~Andrew
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