Re: [Xen-devel] [PATCH V2 1/25] DOMCTL: Introduce new DOMCTL commands for vIOMMU support

[Lan Tianyu <tianyu.lan@xxxxxxxxx>]

On 2017年08月23日 15:22, Roger Pau Monné wrote:
> On Wed, Aug 23, 2017 at 02:06:17PM +0800, Lan Tianyu wrote:
>> Hi Roger:
>>      Thanks for your review.
>>
>> On 2017年08月22日 22:32, Roger Pau Monné wrote:
>>> On Wed, Aug 09, 2017 at 04:34:02PM -0400, Lan Tianyu wrote:
>>>> +
>>>> +/* vIOMMU capabilities */
>>>> +#define VIOMMU_CAP_IRQ_REMAPPING  (1u << 0)
>>>> +
>>>> +struct xen_domctl_viommu_op {
>>>> +    uint32_t cmd;
>>>> +#define XEN_DOMCTL_create_viommu          0
>>>> +#define XEN_DOMCTL_destroy_viommu         1
>>>> +#define XEN_DOMCTL_query_viommu_caps      2
>>>> +    union {
>>>> +        struct {
>>>> +            /* IN - vIOMMU type */
>>>> +            uint64_t viommu_type;
>>>> +            /* 
>>>> +             * IN - MMIO base address of vIOMMU. vIOMMU device models
>>>> +             * are in charge of to check base_address and length.
>>>> +             */
>>>> +            uint64_t base_address;
>>>> +            /* IN - Length of MMIO region */
>>>> +            uint64_t length;
>>>
>>> It seems weird that you can specify the length, is that something
>>> that a user would like to set? Isn't the length of the IOMMU MMIO
>>> region fixed by the hardware spec?
>>
>> Different vendor may have different IOMMU register region sizes. (e.g,
>> VTD has one page size for register region). The length field is to make
>> vIOMMU device model not to abuse address space. Some registers' offsets
>> are reported by other register and these offsets are emulated by vIOMMU
>> device model. If it's not necessary, we can remove it and add it when
>> there is real such requirement.
> 
> So from my understanding the size of the IOMMU MMIO region is implicit
> in the IOMMU type that the user chooses. I don't think this field is
> needed.

OK. Will remove it.

-- 
Best regards
Tianyu Lan

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