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 09:07, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
>> 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. :(
> 
> "25.1.3 Instructions That Cause VM Exits Conditionally" says
> 
> "â IN, INS/INSB/INSW/INSD, OUT, OUTS/OUTSB/OUTSW/OUTSD. The behavior of
> each of these instructions is determined by the settings of the
> âunconditional I/O exitingâ and âuse I/O bitmapsâ VM-execution controls:
> â If both controls are 0, the instruction executes normally. â If the
> âunconditional I/O exitingâ VM-execution control is 1 and the âuse I/O
> bitmapsâ VM-execution control is 0, the instruction causes a VM exit. â
> If the âuse I/O bitmapsâ VM-execution control is 1, the instruction
> causes a VM exit if it attempts to access an I/O port corresponding to a
> bit set to 1 in the appropriate I/O bitmap (see Section 24.6.4). If an
> I/O operation âwraps aroundâ the 16-bit I/O-port space (accesses ports
> FFFFH and 0000H), the I/O instruction causes a VM exit (the
> âunconditional I/O exitingâ VM-execution control is ignored if the âuse
> I/O bitmapsâ VM-execution control is 1)."
> 

Got it. Thanks.

> Jan


Best regards,
Yang

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