Re: [Xen-devel] [PATCH 1/3] x86/HVM: fix forwarding of internally cached requests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.03.16 at 12:49, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 24 March 2016 11:29
>> @@ -196,8 +196,22 @@ int hvm_process_io_intercept(const struc
>>          }
>>      }
>> 
>> -    if ( i != 0 && rc == X86EMUL_UNHANDLEABLE )
>> +    if ( unlikely(rc < 0) )
>>          domain_crash(current->domain);
>> +    else if ( i )
>> +    {
>> +        p->count = i;
>> +        rc = X86EMUL_OKAY;
>> +    }
>> +    else if ( rc == X86EMUL_UNHANDLEABLE )
>> +    {
>> +        /*
>> +         * Don't forward entire batches to the device model: This would
>> +         * prevent the internal handlers to see subsequent iterations of
>> +         * the request.
>> +         */
>> +        p->count = 1;
> 
> I guess this is ok. If stdvga is not caching then the accept function would 
> have failed so you won't get here, and if it send the buffered ioreq then you 
> still don't get here because it returns X86EMUL_OKAY.

Good that you thought of this - I had forgotten that stdvga's
MMIO handling now takes this same code path rather than a
fully separate one. I guess I'll steal some of the wording above
for the v2 commit message.

Jan


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