Re: [Xen-devel] [PATCH] libx86: Introduce wrappers for extracting XCR0/XSS from a cpuid policy

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.05.19 at 13:59, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 23/05/2019 12:52, Jan Beulich wrote:
>>>>> On 23.05.19 at 12:27, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> --- a/xen/include/xen/lib/x86/cpuid.h
>>> +++ b/xen/include/xen/lib/x86/cpuid.h
>>> @@ -308,6 +308,18 @@ static inline void cpuid_featureset_to_policy(
>>>      p->feat._7a1  = fs[FEATURESET_7a1];
>>>  }
>>>  
>>> +static inline uint64_t cpuid_policy_xcr0(const struct cpuid_policy *p)
>>> +{
>>> +    return ((uint64_t)p->xstate.xcr0_high << 32) | p->xstate.xcr0_low;
>>> +}
>>> +
>>> +static inline uint64_t cpuid_policy_xstates(const struct cpuid_policy *p)
>>> +{
>>> +    uint64_t val = p->xstate.xcr0_high | p->xstate.xss_high;
>>> +
>>> +    return (val << 32) | p->xstate.xcr0_low | p->xstate.xss_low;
>>> +}
>> How about also having cpuid_policy_xss() (or cpuid_policy_xss_max())
>> and then simply making cpuid_policy_xstates() combine the two
>> results?
> 
> I started with that, but the resulting code was a little awkward to
> read, and the asm generation was a little worse due to promoting
> everything first.
> 
> I don't think we need cpuid_policy_xss{,_max}() until we actually
> implement something for guests (most likely CET at this rate).

Well, let's stick to what you have then.

Jan



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