Re: [Xen-devel] [PATCH v2] nested VMX: fix I/O port exit emulation

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Jan Beulich wrote on 2013-12-04:
>>>> On 04.12.13 at 02:51, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
>> Jan Beulich wrote on 2013-12-03:
>>> @@ -2220,15 +2219,23 @@ int nvmx_n2_vmexit_handler(struct cpu_us
>>>          if ( ctrl & CPU_BASED_ACTIVATE_IO_BITMAP )
>>>          {
>>>              unsigned long qual;
>>> -            u16 port;
>>> +            u16 port, size;
>>> 
>>>              __vmread(EXIT_QUALIFICATION, &qual);
>>>              port = qual >> 16;
>>> -            bitmap = nvmx->iobitmap[port >> 15];
>>> -            if ( bitmap[(port & 0x7fff) >> 3] & (1 << (port & 0x7)) )
>>> -                nvcpu->nv_vmexit_pending = 1;
>>> +            size = (qual & 7) + 1;
>>> +            do {
>>> +                const u8 *bitmap = nvmx->iobitmap[port >> 15];
>>> +
>>> +                if ( bitmap[(port & 0x7fff) >> 3] & (1 << (port & 7)) )
>>> +                    nvcpu->nv_vmexit_pending = 1;
>>> +                if ( !--size )
>>> +                    break;
>>> +                if ( !++port )
>>> +                    nvcpu->nv_vmexit_pending = 1;
>> 
>> If port overflow, will it cause vmexit or maybe other fault like GP
>> or just be ignored?
> 
> The documentation is explicit here: It causes a VM exit. And hence the
> emulation is doing so too.

Ok. BTW, which chapter tells this? I didn't find the corresponding chapter in 
Intel SDM. :(

> 
>> Also, you need to check the DF bit to know the string direction
>> before updating the port.
> 
> I think Andrew already sufficiently clarified that part.
> 
> Jan


Best regards,
Yang



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