Re: [Xen-devel] [PATCH 2/3] x86emul: check host features alongside guest ones where needed

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/03/2016 08:29, Jan Beulich wrote:
>>>> On 11.03.16 at 18:41, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 11/03/16 17:34, Jan Beulich wrote:
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>
>>> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
>>> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
>>> @@ -1093,6 +1093,22 @@ static bool_t vcpu_has(
>>>  #define vcpu_must_have_cx16() vcpu_must_have(0x00000001, ECX, 13)
>>>  #define vcpu_must_have_avx()  vcpu_must_have(0x00000001, ECX, 28)
>>>  
>>> +#ifdef __XEN__
>>> +/*
>>> + * Note the (subtle?) difference between vcpu_must_have_<feature>() and
>>> + * vcpu_must_have(<feature>): The former only checks guest feature flags,
>>> + * while the latter also checks host ones, i.e. is required to be used when
>>> + * emulation code is using the same instruction class for carrying out the
>>> + * actual operation).
>>> + */
>> This comment is now stale.
>>
>> With this dropped, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> I suppose you're okay with it being adjusted instead of fully dropped:
>
> /*
>  * Note the difference between vcpu_must_have_<feature>() and
>  * host_and_vcpu_must_have(<feature>): The latter needs to be used when
>  * emulation code is using the same instruction class for carrying out
>  * the actual operation.
>  */

Yes - that's great.

~Andrew

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