Re: [Xen-devel] [PATCH 2/2] x86: drop cpu_has_sse{,2}

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/12/16 13:28, Jan Beulich wrote:
>>>> On 09.12.16 at 14:00, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 09/12/16 11:54, Jan Beulich wrote:
>>> Commit dc88221c97 ("x86: rename XMM* features to SSE*") pointlessly
>>> added them - these features are always available on 64-bit CPUs. (Let's
>>> not assume this for MMX though in at least the insn emulator.)
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> This isn't necessarily true when compiled for 32bit in the userspace
>> harness.
> In the test harness vcpu_has_* == cpu_has_*, as also
> demonstrated by
>
> #define host_and_vcpu_must_have(feat) vcpu_must_have(feat)
>
> . The change (as its title is trying to say) really only affects the
> hypervisor.

Right, but this change is still contrary to the written requirement.

/*                                                                              
                                                                                
                        

 * 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.                                                                      
                                                                                
          

 */

We are using SSE and SSE2 instructions for carrying out that emulation,
so should still be using the host_and_vcpu check.

Swapping the hypervisor defines to being 1 will cause the
generate_exception_if() clause to become dead and get dropped, turning
host_and_vcpu_must_have() into just vcpu_must_have_##feat

~Andrew

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