Re: [PATCH 3/4] x86: Allow non-faulting accesses to non-emulated MSRs if policy permits this

[boris.ostrovsky@xxxxxxxxxx]

On 1/11/21 2:48 AM, Jan Beulich wrote:
> On 08.01.2021 21:39, boris.ostrovsky@xxxxxxxxxx wrote:
>> On 1/8/21 10:18 AM, Jan Beulich wrote:
>>
>>>
>>> Just to re-raise the question raised by Andrew already earlier
>>> on: Has Solaris been fixed in the meantime, or is this at least
>>> firmly planned to happen?
>> I was told they will open a bug.
> "Will", not "did"?


I can't say for sure, I don't have access to their bugDB, they typically keep 
bugs private (or so I am told). All I can say is that they are aware of this 
issue.


>
>>> @@ -3319,10 +3319,8 @@ static int vmx_msr_write_intercept(unsigned int msr, 
>>> uint64_t msr_content)
>>>               is_last_branch_msr(msr) )
>>>              break;
>>>  
>>> -        gdprintk(XENLOG_WARNING,
>>> -                 "WRMSR 0x%08x val 0x%016"PRIx64" unimplemented\n",
>>> -                 msr, msr_content);
>>> -        goto gp_fault;
>>> +        if ( guest_unhandled_msr(v, msr, &msr_content, true) )
>>> +            goto gp_fault;
>>>      }
>>>  
>>>      return X86EMUL_OKAY;
>>> These functions also get used from the insn emulator, when it
>>> needs to fetch an MSR value (not necessarily in the context of
>>> emulating RDMSR or WRMSR). I wonder whether applying this
>>> behavior in that case is actually correct. It would only be if
>>> we would settle on it being a requirement that any such MSRs
>>> have to have emulation present in one of the handlers.
>>
>> Hmm.. Yes, I did not consider this. I am not convinced this will
>> always result in correct behavior for the emulator so I will
>> need to pass down a parameter. Unless there is a way to figure
>> out whether we are running in the emulator (which I don't
>> immediately see)
> Passing a parameter for this is sort of ugly, but I presume
> unavoidable. The more that what you need to know is not "running
> in emulator", but "guest RDMSR/WRMSR" - this can also happen
> through the emulator.


Right, that's what I meant.


-boris