Re: [PATCH v3 02/16] iommu: Introduce cache_invalidate API

Auger Eric
2019-05-14T07:36:52Z

Hi Jacob,

On 5/14/19 12:16 AM, Jacob Pan wrote:
> On Mon, 13 May 2019 18:09:48 +0100
> Jean-Philippe Brucker <jean-philippe.brucker@arm.com> wrote:
>
>> On 13/05/2019 17:50, Auger Eric wrote:
>>>> struct iommu_inv_pasid_info {
>>>> #define IOMMU_INV_PASID_FLAGS_PASID (1 << 0)
>>>> #define IOMMU_INV_PASID_FLAGS_ARCHID (1 << 1)
>>>> __u32 flags;
>>>> __u32 archid;
>>>> __u64 pasid;
>>>> };
>>> I agree it does the job now. However it looks a bit strange to do a
>>> PASID based invalidation in my case - SMMUv3 nested stage - where I
>>> don't have any PASID involved.
>>>
>>> Couldn't we call it context based invalidation then? A context can
>>> be tagged by a PASID or/and an ARCHID.
>>
>> I think calling it "context" would be confusing as well (I shouldn't
>> have used it earlier), since VT-d uses that name for device table
>> entries (=STE on Arm SMMU). Maybe "addr_space"?
>>
> I am still struggling to understand what ARCHID is after scanning
> through SMMUv3.1 spec. It seems to be a constant for a given SMMU. Why
> do you need to pass it down every time? Could you point to me the
> document or explain a little more on ARCHID use cases.
> We have three fileds called pasid under this struct
> iommu_cache_invalidate_info{}
> Gets confusing :)
archid is a generic term. That's why you did not find it in the spec ;-)

On ARM SMMU the archid is called the ASID (Address Space ID, up to 16
bits. The ASID is stored in the Context Descriptor Entry (your PASID
entry) and thus characterizes a given stage 1 translation
"context"/"adress space".

At the moment the ASID is allocated per iommu domain. With aux domains
we should have one ASID per aux domain, Jean-Philippe said.

ASID tags IOTLB S1 entries. As the ASID is part of the "context
descriptor" which is owned by the guest, the API must pass it somehow.

4.4.1.2 CMD_TLBI_NH_ASID(VMID, ASID) invalidation command allows to
invalidate all IOTLB S1 entries for a given VMID/ASID and this is the
functionality which is currently missing in the API. This is not an
address based invalidation or a "pure" PASID based invalidation. At the
moment we don't support PASIDs on ARM and I need this capability.

Thanks

Eric

>> Thanks,
>> Jean
>>
>>>
>>> Domain invalidation would invalidate all the contexts belonging to
>>> that domain.
>>>
>>> Thanks
>>>
>>> Eric
>
> [Jacob Pan]