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

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Message-ID: <8a3b8fcd-48c4-7d9e-7672-e73431bcde5b@arm.com>
Date:   Mon, 3 Sep 2018 13:28:03 +0100
From:   Jean-Philippe Brucker <jean-philippe.brucker@....com>
To:     Auger Eric <eric.auger@...hat.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

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.

> 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,
};

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 = ...
};

Thanks,
Jean