Re: [Xen-devel] [PATCH V3 1/3] xen/mem_access: Support for memory-content hiding

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.07.15 at 17:32, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 07/07/2015 04:27 PM, Jan Beulich wrote:
>>>>> On 06.07.15 at 17:51, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> @@ -1552,9 +1556,15 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned 
>>> long gla,
>>>  
>>>      if ( v->arch.vm_event.emulate_flags )
>>>      {
>>> -        hvm_mem_access_emulate_one((v->arch.vm_event.emulate_flags &
>>> -                                    MEM_ACCESS_EMULATE_NOWRITE) != 0,
>>> -                                   TRAP_invalid_op, 
>>> HVM_DELIVER_NO_ERROR_CODE);
>>> +        enum emul_kind kind = EMUL_KIND_NORMAL;
>>> +
>>> +        if ( v->arch.vm_event.emulate_flags & 
>>> MEM_ACCESS_SET_EMUL_READ_DATA )
>>> +            kind = EMUL_KIND_SET_CONTEXT;
>>> +        else if ( v->arch.vm_event.emulate_flags & 
>>> MEM_ACCESS_EMULATE_NOWRITE )
>> 
>> Is there code in place rejecting both flags being set at once? I don't
>> recall having seen any...
> 
> No, there isn't. Both flags can be set at once, but if so only the
> SET_EMUL_READ_DATA will be honored.

But to me, purely theoretically setting both flags together makes
sense, and hence this combination, if it isn't working today,
shouldn't result in unexpected behavior (perhaps differing from
what a future Xen version might do).

Jan


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