Re: [PATCH v2 3/4] x86: Allow non-faulting accesses to non-emulated MSRs if policy permits this

[Jan Beulich <jbeulich@suse.com>]

On 26.01.2021 17:02, Boris Ostrovsky wrote:
> On 21-01-26 10:05:47, Jan Beulich wrote:
>> On 25.01.2021 19:42, Boris Ostrovsky wrote:
>>> On 21-01-25 11:22:08, Jan Beulich wrote:
>>>> On 22.01.2021 20:52, Boris Ostrovsky wrote:
>>>>> "Sibling" in terms of name (yes, it would be) or something else?
>>>>
>>>> Name and (possible) purpose - a validate hook could want to
>>>> make use of this, for example.
>>>
>>> A validate hook? 
>>
>> Quoting from struct x86_emulate_ops:
>>
>>     /*
>>      * validate: Post-decode, pre-emulate hook to allow caller controlled
>>      * filtering.
>>      */
>>     int (*validate)(
>>         const struct x86_emulate_state *state,
>>         struct x86_emulate_ctxt *ctxt);
>>
>> Granted to be directly usable the function would need to have a
>> "state" parameter. As that's unused, having it have one and
>> passing NULL in your case might be acceptable. But I also could
>> see arguments towards this not being a good idea.
> 
> I see. Where would we need to call this hook though? We are never directly
> emulating MSR access (compared to, for example, CR accesses where
> x86_insn_is_cr_access is used). And for PV we already validate it in
> emul-priv-op.c():validate().

If you look at some of the functions used for this hook, you may
realize that what your function does could also fit a hypothetical
future hook. Hence I was suggesting to make the new function
suitable for such use right away (and in particular fit their
naming scheme). But it looks like this has ended up more confusing
than anything else, so never mind.

Jan