linux-kernel - Re: [PATCH v4 1/2] iommu/arm-smmu-v3: Match Stall behaviour for S2

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Message-ID: <20240830202051.GA3468552@ziepe.ca>
Date: Fri, 30 Aug 2024 17:20:51 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mostafa Saleh <smostafa@...gle.com>
Cc: linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, will@...nel.org,
	robin.murphy@....com, joro@...tes.org, jean-philippe@...aro.org,
	nicolinc@...dia.com, mshavit@...gle.com
Subject: Re: [PATCH v4 1/2] iommu/arm-smmu-v3: Match Stall behaviour for S2

On Fri, Aug 30, 2024 at 11:03:47AM +0000, Mostafa Saleh wrote:
> According to the spec (ARM IHI 0070 F.b), in
> "5.5 Fault configuration (A, R, S bits)":
>     A STE with stage 2 translation enabled and STE.S2S == 0 is
>     considered ILLEGAL if SMMU_IDR0.STALL_MODEL == 0b10.
> 
> Also described in the pseudocode “SteIllegal()”
>     if STE.Config == '11x' then
>         [..]
>         if eff_idr0_stall_model == '10' && STE.S2S == '0' then
>             // stall_model forcing stall, but S2S == 0
>             return TRUE;
> 
> Which means, S2S must be set when stall model is
> "ARM_SMMU_FEAT_STALL_FORCE", but currently the driver ignores that.
> 
> Although, the driver can do the minimum and only set S2S for
> “ARM_SMMU_FEAT_STALL_FORCE”, it is more consistent to match S1
> behaviour, which also sets it for “ARM_SMMU_FEAT_STALL” if the
> master has requested stalls.

Hum, that is looking a bit out of date
perhaps. ARM_SMMU_FEAT_STALL_FORCE should definately set stall, but
for stall-optional it should probably only be set if a faulting type
domain is installed (probably on a PASID)..

Still looks Ok

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason