Re: [PATCH v1 03/17] intel_iommu: Add a placeholder variable for scalable modern mode

[CLEMENT MATHIEU--DRIF <clement.mathieu--drif@eviden.com>]

On 19/07/2024 05:39, Duan, Zhenzhong wrote:
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>
>> -----Original Message-----
>> From: Duan, Zhenzhong]
>> Subject: RE: [PATCH v1 03/17] intel_iommu: Add a placeholder variable for
>> scalable modern mode
>>
>>
>>
>>> -----Original Message-----
>>> From: Liu, Yi L <yi.l.liu@intel.com>
>>> Subject: Re: [PATCH v1 03/17] intel_iommu: Add a placeholder variable for
>>> scalable modern mode
>>>
>>> On 2024/7/19 10:47, Duan, Zhenzhong wrote:
>>>>
>>>>> -----Original Message-----
>>>>> From: CLEMENT MATHIEU--DRIF <clement.mathieu--drif@eviden.com>
>>>>> Subject: Re: [PATCH v1 03/17] intel_iommu: Add a placeholder variable
>>> for
>>>>> scalable modern mode
>>>>>
>>>>>
>>>>>
>>>>> On 18/07/2024 10:16, Zhenzhong Duan wrote:
>>>>>> Caution: External email. Do not open attachments or click links, unless
>>> this
>>>>> email comes from a known sender and you know the content is safe.
>>>>>>
>>>>>> Add an new element scalable_mode in IntelIOMMUState to mark
>>> scalable
>>>>>> modern mode, this element will be exposed as an intel_iommu
>> property
>>>>>> finally.
>>>>>>
>>>>>> For now, it's only a placehholder and used for cap/ecap initialization,
>>>>>> compatibility check and block host device passthrough until nesting
>>>>>> is supported.
>>>>>>
>>>>>> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
>>>>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>>>>> ---
>>>>>>     hw/i386/intel_iommu_internal.h |  2 ++
>>>>>>     include/hw/i386/intel_iommu.h  |  1 +
>>>>>>     hw/i386/intel_iommu.c          | 34 +++++++++++++++++++++++-------
>> --
>>> --
>>>>>>     3 files changed, 26 insertions(+), 11 deletions(-)
>>>>>>
>>>>>> diff --git a/hw/i386/intel_iommu_internal.h
>>>>> b/hw/i386/intel_iommu_internal.h
>>>>>> index c0ca7b372f..4e0331caba 100644
>>>>>> --- a/hw/i386/intel_iommu_internal.h
>>>>>> +++ b/hw/i386/intel_iommu_internal.h
>>>>>> @@ -195,6 +195,7 @@
>>>>>>     #define VTD_ECAP_PASID              (1ULL << 40)
>>>>>>     #define VTD_ECAP_SMTS               (1ULL << 43)
>>>>>>     #define VTD_ECAP_SLTS               (1ULL << 46)
>>>>>> +#define VTD_ECAP_FLTS               (1ULL << 47)
>>>>>>
>>>>>>     /* CAP_REG */
>>>>>>     /* (offset >> 4) << 24 */
>>>>>> @@ -211,6 +212,7 @@
>>>>>>     #define VTD_CAP_SLLPS               ((1ULL << 34) | (1ULL << 35))
>>>>>>     #define VTD_CAP_DRAIN_WRITE         (1ULL << 54)
>>>>>>     #define VTD_CAP_DRAIN_READ          (1ULL << 55)
>>>>>> +#define VTD_CAP_FS1GP               (1ULL << 56)
>>>>>>     #define VTD_CAP_DRAIN               (VTD_CAP_DRAIN_READ |
>>>>> VTD_CAP_DRAIN_WRITE)
>>>>>>     #define VTD_CAP_CM                  (1ULL << 7)
>>>>>>     #define VTD_PASID_ID_SHIFT          20
>>>>>> diff --git a/include/hw/i386/intel_iommu.h
>>>>> b/include/hw/i386/intel_iommu.h
>>>>>> index 1eb05c29fc..788ed42477 100644
>>>>>> --- a/include/hw/i386/intel_iommu.h
>>>>>> +++ b/include/hw/i386/intel_iommu.h
>>>>>> @@ -262,6 +262,7 @@ struct IntelIOMMUState {
>>>>>>
>>>>>>         bool caching_mode;              /* RO - is cap CM enabled? */
>>>>>>         bool scalable_mode;             /* RO - is Scalable Mode supported?
>> */
>>>>>> +    bool scalable_modern;           /* RO - is modern SM supported? */
>>>>>>         bool snoop_control;             /* RO - is SNP filed supported? */
>>>>>>
>>>>>>         dma_addr_t root;                /* Current root table pointer */
>>>>>> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
>>>>>> index 1cff8b00ae..40cbd4a0f4 100644
>>>>>> --- a/hw/i386/intel_iommu.c
>>>>>> +++ b/hw/i386/intel_iommu.c
>>>>>> @@ -755,16 +755,20 @@ static inline bool
>>>>> vtd_is_level_supported(IntelIOMMUState *s, uint32_t level)
>>>>>>     }
>>>>>>
>>>>>>     /* Return true if check passed, otherwise false */
>>>>>> -static inline bool vtd_pe_type_check(X86IOMMUState *x86_iommu,
>>>>>> -                                     VTDPASIDEntry *pe)
>>>>>> +static inline bool vtd_pe_type_check(IntelIOMMUState *s,
>>>>> VTDPASIDEntry *pe)
>>>>>>     {
>>>>> What about using the cap/ecap registers to know if the translation types
>>>>> are supported or not.
>>>>> Otherwise, we could add a comment to explain why we expect
>>>>> s->scalable_modern to give us enough information.
>>>> What about below:
>>>>
>>>> /*
>>>>    *VTD_ECAP_FLTS in ecap is set if s->scalable_modern is true, or else
>>> VTD_ECAP_SLTS can be set or not depending on s->scalable_mode.
>>>>    *So it's simpler to check s->scalable_modern directly for a PASID entry
>>> type instead ecap bits.
>>>>    */
>>> Since this helper is for pasid entry check, so you can just return false
>>> if the pe's PGTT is SS-only.
>> It depends on which scalable mode is chosed.
>> In scalable legacy mode, PGTT is SS-only and we should return true.
>>
>>> It might make more sense to check the ecap/cap here as anyhow the
>>> capability is listed in ecap/cap. This may also bring us some convenience.
>>>
>>> Say in the future, if we want to add a new mode (e.g. scalable mode 2.0)
>>> that supports both FS and SS for guest, we may need to update this helper
>>> as well if we check the scalable_modern. But if we check the ecap/cap, then
>>> the future change just needs to control the ecap/cap setting at the
>>> beginning of the vIOMMU init. To keep the code aligned, you may need to
>>> check ecap.PT bit for VTD_SM_PASID_ENTRY_PT. :)
>> OK, will be like below:
>>
>> --- a/hw/i386/intel_iommu.c
>> +++ b/hw/i386/intel_iommu.c
>> @@ -826,14 +826,14 @@ static inline bool
>> vtd_pe_type_check(IntelIOMMUState *s, VTDPASIDEntry *pe)
>>
>>      switch (VTD_PE_GET_TYPE(pe)) {
>>      case VTD_SM_PASID_ENTRY_FLT:
>> -        return s->scalable_modern;
>> +        return !!(s->ecap & VTD_ECAP_FLTS);
>>      case VTD_SM_PASID_ENTRY_SLT:
>> -        return !s->scalable_modern;
>> +        return !!(s->ecap & VTD_ECAP_FLTS) || !(s->ecap & VTD_ECAP_SMTS);
> Sorry typo err, should be:
>
> +        return !!(s->ecap & VTD_ECAP_SLTS) || !(s->ecap & VTD_ECAP_SMTS);
>
I agree with Yi's point of view, this version looks good
>>      case VTD_SM_PASID_ENTRY_NESTED:
>>          /* Not support NESTED page table type yet */
>>          return false;
>>      case VTD_SM_PASID_ENTRY_PT:
>> -        return x86_iommu->pt_supported;
>> +        return !!(s->ecap & VTD_ECAP_PT);
>>      default:
>>          /* Unknown type */
>>          return false;
>>
>> Thanks
>> Zhenzhong