Re: [Xen-devel] hvmemul_rep_movs() vs MMIO

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.09.13 at 14:47, Tim Deegan <tim@xxxxxxx> wrote:
> At 13:41 +0100 on 20 Sep (1379684515), Jan Beulich wrote:
>> >>> On 20.09.13 at 14:05, Tim Deegan <tim@xxxxxxx> wrote:
>> > At 12:46 +0100 on 20 Sep (1379681171), Jan Beulich wrote:
>> >> Tim,
>> >> 
>> >> was it really intended for "x86/hvm: use unlocked p2m lookups in
>> >> hvmemul_rep_movs()" to special case p2m_mmio_dm but not
>> >> p2m_mmio_direct?
>> > 
>> > Hmm.  It certainly doesn't seem to handle that case very well now, but
>> > I'm not sure the code before was any better.  AFAICT it would have
>> > passed mmio_direct accesses to hvmemul_do_mmio(), which would send them
>> > to qemu.
>> 
>> Hmm, wait - if MMIO of a passed through device, other than for
>> its port I/O, doesn't get intercepted at all, but instead gets taken
>> care of by there being a valid gfn->mfn translation in place, then
>> indeed before and after your change things aren't handled well.
>> Perhaps we should bail from there if either side is p2m_mmio_direct
>> as well as if both sides are p2m_mmio_dm:
> 
> Sounds OK to me.  Clearly mmio-mmio string operations aren't something
> we need to make go fast. :)

Who knows: Frame buffer internal moves might e.g. be desirable
to get accelerated. But if we want to do such, be need to honor
the original access size at the very least.

> Reviewed-by: Tim Deegan <tim@xxxxxxx>

Actually the final patch is to be bigger - we need to do something
similar in rep_ins and rep_outs. Will send the whole thing in a few
minutes (after smoke testing).

Jan

>> --- a/xen/arch/x86/hvm/emulate.c
>> +++ b/xen/arch/x86/hvm/emulate.c
>> @@ -799,6 +799,10 @@ static int hvmemul_rep_movs(
>>      (void) get_gfn_query_unlocked(current->domain, sgpa >> PAGE_SHIFT, 
>> &sp2mt);
>>      (void) get_gfn_query_unlocked(current->domain, dgpa >> PAGE_SHIFT, 
>> &dp2mt);
>>  
>> +    if ( sp2mt == p2m_mmio_direct || dp2mt == p2m_mmio_direct ||
>> +         (sp2mt == p2m_mmio_dm && dp2mt == p2m_mmio_dm) )
>> +        return X86EMUL_UNHANDLEABLE;
>> +
>>      if ( sp2mt == p2m_mmio_dm )
>>          return hvmemul_do_mmio(
>>              sgpa, reps, bytes_per_rep, dgpa, IOREQ_READ, df, NULL);
>> 
>> Jan
>> 




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