linux-kernel - Re: [PATCH v3 02/16] iommu: Introduce cache

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Message-ID: <0da76e57-76f6-06fa-d34e-30cd0c294984@redhat.com>
Date:   Tue, 14 May 2019 09:36:40 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>
Cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Andriy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v3 02/16] iommu: Introduce cache_invalidate API

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@....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]
>