Re: [Xen-devel] [PATCH V2 11/25] x86/hvm: Introduce a emulated VTD for HVM

[Lan Tianyu <tianyu.lan@xxxxxxxxx>]

On 2017年08月24日 16:49, Roger Pau Monné wrote:
> On Thu, Aug 24, 2017 at 10:16:32AM +0800, Lan Tianyu wrote:
>> On 2017年08月23日 15:58, Roger Pau Monné wrote:
>>> On Wed, Aug 09, 2017 at 04:34:12PM -0400, Lan Tianyu wrote:
>>>> From: Chao Gao <chao.gao@xxxxxxxxx>
>>>> +}
>>>> +
>>>> +#define vvtd_get_reg_quad(vvtd, reg, val) do {  \
>>>> +    (val) = vvtd_get_reg(vvtd, (reg) + 4 );     \
>>>> +    (val) = (val) << 32;                        \
>>>> +    (val) += vvtd_get_reg(vvtd, reg);           \
>>>> +} while(0)
>>>> +#define vvtd_set_reg_quad(vvtd, reg, val) do {  \
>>>> +    vvtd_set_reg(vvtd, reg, (val));             \
>>>> +    vvtd_set_reg(vvtd, (reg) + 4, (val) >> 32); \
>>>> +} while(0)
>>>
>>> You seem to need to access hvm_hw_vvtd_regs using different sizes, why
>>> not do:
>>>
>>> union hvm_hw_vvtd_regs {
>>>     uint8_t  data8[1024];
>>>     uint16_t data16[512];
>>>     uint32_t data32[256];
>>>     uint64_t data64[128];
>>> };
>>>
>>> Then the access is much more straightforward and you don't need the
>>> complicated helpers that you have above.
>>
>> Yes, that will be simpler.
> 
> Keep in mind (as said in another patch) that this approach will only
> work correctly as long as you force accesses to be size aligned, which
> you where not doing now.
> 
> I've looked at the VT-d spec, but I cannot find any section that
> explains the restrictions on access sizes and alignments.
> 

10.2 Software Access to Registers?

-- 
Best regards
Tianyu Lan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel