Re: [Xen-devel] [PATCH RFC 20/31] x86: Improvements to in-hypervisor cpuid sanity checks

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.01.16 at 19:15, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 21/01/16 17:21, Andrew Cooper wrote:
>> On 21/01/16 17:02, Jan Beulich wrote:
>>>>>> On 16.12.15 at 22:24, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>>      case 0x80000001:
>>>> -        /* Modify Feature Information. */
>>>> -        if ( is_pv_32bit_domain(currd) )
>>>> -        {
>>>> -            __clear_bit(X86_FEATURE_LM % 32, &d);
>>>> -            __clear_bit(X86_FEATURE_LAHF_LM % 32, &c);
>>>> -        }
>>>> -        if ( is_pv_32bit_domain(currd) &&
>>>> -             boot_cpu_data.x86_vendor != X86_VENDOR_AMD )
>>>> -            __clear_bit(X86_FEATURE_SYSCALL % 32, &d);
>>> But what about these 32-bit specific removals?
>> LM, from the deep feature dependency removal in libxc, when it is known
>> that the domain is 32bit.
>>
>> For SYSCALL, as far as I can tell, the logic is wrong.  32bit compat
>> mode code on Intel can use SYSCALL, as Xen is running in Long mode. 
>> (This is opposite to the AMD case where 32bit compat code cannot use
>> SYSENTER, because Xen is in Long mode.)
> 
> I have just double checked.  32bit PV guests on Intel definitely can use
> syscall.

Double checked where? As just said in the other mail, I can't find
documentation of CSTAR being implemented anywhere in SDM Vol 3.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel