Re: [Xen-devel] [PATCH 2/9] x86/pv: Support do_set_segment_base() for compat guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.08.16 at 15:25, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 02/08/16 13:52, Jan Beulich wrote:
>>>>> On 18.07.16 at 11:51, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> set_segment_base is the only hypercall exists in only one of the two modes
>>> guests might run in; all other hypercalls are either implemented, or
>>> unimplemented in both modes.
>>>
>>> Remove this split, by allowing do_set_segment_base() to be called in the
>>> compat hypercall path.  This change will simplify the verification logic in 
>>> a
>>> later change.
>>>
>>> No behavioural change from a guests point of view.
>> Nevertheless I don't view this as a reasonable change on its own:
> 
> Why not?  It is far better to call it out in isolation, than to mix it
> in with an already-existing complicated change.

If the changes here were anywhere near being themselves
complicated, I'd agree.

>>> --- a/xen/arch/x86/x86_64/compat/entry.S
>>> +++ b/xen/arch/x86/x86_64/compat/entry.S
>>> @@ -453,7 +453,7 @@ ENTRY(compat_hypercall_table)
>>>          .quad compat_update_va_mapping_otherdomain
>>>          .quad compat_iret
>>>          .quad compat_vcpu_op
>>> -        .quad compat_ni_hypercall       /* 25 */
>>> +        .quad do_set_segment_base       /* 25 */
>> This part will (I suppose) be deleted by a later change.
> 
> When moved into C, it will be hidden behind the macros used to construct
> both table values at once.

And compat_set_segment_base could then just be #define-d to NULL.

Jan


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