linux-kernel - Re: [RFC PATCH v1 2/8] iommu/arm-smmu-v3: Perform invalidations over installed

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Date:   Thu, 17 Aug 2023 16:20:00 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Michael Shavit <mshavit@...gle.com>
Cc:     iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, will@...nel.org, nicolinc@...dia.com,
        tina.zhang@...el.com, jean-philippe@...aro.org,
        robin.murphy@....com
Subject: Re: [RFC PATCH v1 2/8] iommu/arm-smmu-v3: Perform invalidations over
 installed_smmus

On Fri, Aug 18, 2023 at 02:16:24AM +0800, Michael Shavit wrote:
> Prepare and batch invalidation commands for each SMMU that a domain is
> installed onto.
> Move SVA's check against the smmu's ARM_SMMU_FEAT_BTM bit into
> arm_smmu_tlb_inv_range_asid so that it can be checked against each
> installed SMMU.
> 
> Signed-off-by: Michael Shavit <mshavit@...gle.com>
> ---
> It's not obvious to me whether skipping the tlb_inv_range_asid when
> ARM_SMMU_FEAT_BTM is somehow specific to SVA? Is moving the check into
> arm_smmu_tlb_inv_range_asid still valid if that function were called
> outside of SVA?

Logically it should be linked to SVA, and specifically to the mmu
notifier callback. The mmu notifier callback is done whenever the CPU
did an invalidation and BTM means the SMMU tracks exactly those
automatically. Thus we don't need to duplicated it. Indeed, we should
probably not even register a mmu notifier on BTM capable devices.

It is certainly wrong to skip invalidations generated for any other
reason.

>From what I can tell SVA domains should have their CD table entry
programmed with "ASET=0" and normal paging domains should be
programmed with "ASET=1". This causes only the SVA domains to listen
to the BTM invalidations.

Jason