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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 04/12/2013 01:51, Zhang, Yang Z wrote:
> Jan Beulich wrote on 2013-12-03:
>> For multi-byte operations all affected ports' bits in the bitmap need to be
>> checked, not just the first port's one.
>>
>> Reported-by: Matthew Daley <mattd@xxxxxxxxxxx>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> v2: Fix loop construct.
>>
>> --- a/xen/arch/x86/hvm/vmx/vvmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vvmx.c
>> @@ -2134,7 +2134,6 @@ int nvmx_n2_vmexit_handler(struct cpu_us
>>      struct nestedvcpu *nvcpu = &vcpu_nestedhvm(v);
>>      struct nestedvmx *nvmx = &vcpu_2_nvmx(v);
>>      u32 ctrl;
>> -    u8 *bitmap;
>>
>>      nvcpu->nv_vmexit_pending = 0;
>>      nvmx->intr.intr_info = 0;
>> @@ -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? Also, you need to check the DF bit to know the string direction 
> before updating the port.
>
> Best regards,
> Yang
>
>

What does the direction flag have to do with the port(s) used as the
target of an ins/outs instruction?  I was under the impression that it
solely acted as an increment/decrement on si/di.

~Andrew

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