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 20:41:08 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        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
Subject: Re: [RFC PATCH v1 2/8] iommu/arm-smmu-v3: Perform invalidations over
 installed_smmus

On 2023-08-17 20:20, Jason Gunthorpe wrote:
> 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.

Almost - broadcast invalidates from the CPU only apply to SMMU TLBs; we 
still need the notifier for the sake of issuing ATC invalidate commands 
to endpoints.

> 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.

Correct.

Thanks,
Robin.