linux-kernel - Re: [RFC 02/13] iommu: Introduce tlb

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Date:   Mon, 3 Sep 2018 14:41:46 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        "eric.auger.pro@...il.com" <eric.auger.pro@...il.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu, joro@...tes.org,
        alex.williamson@...hat.com, jacob.jun.pan@...ux.intel.com,
        "yi.l.liu\""@linux.intel.com, will.deacon@....com,
        robin.murphy@....com
Cc:     marc.zyngier@....com, peter.maydell@...aro.org,
        christoffer.dall@....com
Subject: Re: [RFC 02/13] iommu: Introduce tlb_invalidate API

Hi Jean-Philippe,
On 09/03/2018 02:28 PM, Jean-Philippe Brucker wrote:
> On 31/08/2018 15:07, Auger Eric wrote:
>>> Since the ioctl will be used to combine invalidations (invalidate both
>>> ATC and TLB with a single call), we need an additional ASID field for
>>> the SMMU - ATC is invalidated by PASID, TLB by ASID. I used to call it
>>> "tag", but I'm leaning towards "arch_id" now
>>> (http://www.linux-arm.org/git?p=linux-jpb.git;a=commitdiff;h=40fdef74816dd8d8d113100b9e0162fab4cec28d)
>>
>> I aknowledge I am not crystal clear about that. for a given iommu_domain
>> don't you have a single asid. Can't you retrieve the asid from the
>> iommu_domain/arm_smmu_domain/arm_smmu_s1_cfg/arm_smmu_ctx_desc.asid?
>> Here again I am confused bout the dual iommu_domain/struct device
>> parameters.
> 
> In nested mode, ASIDs are allocated by the guest and written into the CD
> table. Even if there is a single CD it will still be private to the
> guest. When receiving the invalidation, the host could walk the CD
> tables to retrieve the ASID, but it's not guaranteed to be here anymore:
> the guest could well clear a CD before sending the invalidate command.

That's fully correct. I messed up at the beginning with this asid and
that's perfectly true the asid needs to be passed. I will respin
accordingly.

> 
>> I have another trouble while doing the QEMU integration.
>> When the guests does an NH_ALL, this propagates an invalidation on the
>> whole IPA range and we must discriminate that from regular NH_VA calls.
>> How would you encode the NH_ALL with this API?
> 
> I think that translates to an invalidate-all for the domain:
> 
> struct tlb_iommu_invalidate_info info = {
> 	.hdr.type = IOMMU_INV_TYPE_TLB,
> 	.granularity = IOMMU_INV_GRANU_DOMAIN_ALL_PASID,
OK
> };
> 
> Reading the spec again, I though the API was missing a way to encode
> TLBI_NH_VAA, invalidate a range for all ASIDs. Although it feels
> contrived, we could represent it with the following:
> 
> struct tlb_iommu_invalidate_info info = {
> 	.hdr.type = IOMMU_INV_TYPE_TLB,
> 	.granularity = IOMMU_INV_GRANU_PAGE_PASID,
> 	.flags = IOMMU_INVALIDATE_GLOBAL_PAGE,
> 	.addr = ...
OK

Also what about CMD_CFI_CD(_ALL) propagation. Is it an
IOMMU_INV_TYPE_PASID invalidation?

Thanks

Eric
> };
> 
> Thanks,
> Jean
>