Re: [Xen-devel] [PATCH 5/3] x86/shadow: emulate_gva_to_mfn() should respect p2m_ioreq_server

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.11.18 at 11:59, <Paul.Durrant@xxxxxxxxxx> wrote:
>>  -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 13 November 2018 10:47
>> To: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Paul Durrant
>> <Paul.Durrant@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Tim (Xen.org)
>> <tim@xxxxxxx>
>> Subject: [PATCH 5/3] x86/shadow: emulate_gva_to_mfn() should respect
>> p2m_ioreq_server
>> 
>> Writes to such pages would need to be handed to the emulator, which we're
>> not prepared to do at this point.
>> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> 
>> --- a/xen/arch/x86/mm/shadow/hvm.c
>> +++ b/xen/arch/x86/mm/shadow/hvm.c
>> @@ -338,7 +338,7 @@ static mfn_t emulate_gva_to_mfn(struct v
>>      {
>>          return _mfn(BAD_GFN_TO_MFN);
>>      }
>> -    if ( p2m_is_discard_write(p2mt) )
>> +    if ( p2m_is_discard_write(p2mt) || p2mt == p2m_ioreq_server )
>>      {
>>          put_page(page);
>>          return _mfn(READONLY_GFN);
> 
> Is this what we want here? I would have thought we want to return 
> BAD_GFN_TO_MFN in the p2m_ioreq_server case so that the caller treats this in 
> the same way it would MMIO.

I'm not sure which behavior is better; I'm certainly fine with switching
as you say, but I'd first like to see Tim's opinion as well.

Jan



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