linux-kernel - Re: [PATCH 1/1] iommu/arm-smmu: Fix for ThunderX erratum #27704

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Date:   Thu, 19 Jan 2017 16:16:16 +0000
From:   Will Deacon <will.deacon@....com>
To:     Tomasz Nowicki <tn@...ihalf.com>
Cc:     robin.murphy@....com, mark.rutland@....com, joro@...tes.org,
        Linu.Cherian@...ium.com, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Sunil.Goutham@...ium.com, Geethasowjanya.Akula@...ium.com,
        Tirumalesh.Chalamarla@...ium.com, Prasun.Kapoor@...ium.com
Subject: Re: [PATCH 1/1] iommu/arm-smmu: Fix for ThunderX erratum #27704

On Mon, Jan 16, 2017 at 08:16:07AM +0100, Tomasz Nowicki wrote:
> The goal of erratum #27704 workaround was to make sure that ASIDs and VMIDs
> are unique across all SMMU instances on affected Cavium systems.
> 
> Currently, the workaround code partitions ASIDs and VMIDs by increasing
> global cavium_smmu_context_count which in turn becomes the base ASID and VMID
> value for the given SMMU instance upon the context bank initialization.
> 
> For systems with multiple SMMU instances this approach implies the risk
> of crossing 8-bit ASID, like for 1-socket CN88xx capable of 4 SMMUv2,
> 128 context banks each:
> SMMU_0 (0-127 ASID RANGE)
> SMMU_1 (127-255 ASID RANGE)
> SMMU_2 (256-383 ASID RANGE) <--- crossing 8-bit ASID
> SMMU_3 (384-511 ASID RANGE) <--- crossing 8-bit ASID
> 
> Since now we use 8-bit ASID (SMMU_CBn_TCR2.AS = 0) we effectively misconfigure
> ASID[15:8] bits of SMMU_CBn_TTBRm register for SMMU_2/3. Moreover, we still
> assume non-zero ASID[15:8] bits upon context invalidation. In the end,
> except SMMU_0/1 devices all other devices under other SMMUs will fail on guest
> power off/on. Since we try to invalidate TLB with 16-bit ASID but we actually
> have 8-bit zero padded 16-bit entry.
> 
> This patch adds 16-bit ASID support for stage-1 AArch64 contexts so that
> we use ASIDs consistently for all SMMU instances.
> 
> Signed-off-by: Tomasz Nowicki <tn@...ihalf.com>
> Reviewed-by: Robin Murphy <robin.murphy@....com>
> Reviewed-by: Tirumalesh Chalamarla  <Tirumalesh.Chalamarla@...ium.com>
> ---
>  drivers/iommu/arm-smmu.c | 3 +++
>  1 file changed, 3 insertions(+)

Thanks, queued for 4.11.

Will