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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.
 */

Jan


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