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

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Message-ID: <20240816133135.GP3468552@ziepe.ca>
Date: Fri, 16 Aug 2024 10:31:35 -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 v3] iommu/arm-smmu-v3: Match Stall behaviour for S2

On Fri, Aug 16, 2024 at 12:59:01PM +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 at the moment 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.
> 
> Also, since S2 stalls are enabled now, report them to the IOMMU layer
> and for VFIO devices it will fail anyway as VFIO doesn’t register an
> iopf handler.
> 
> Signed-off-by: Mostafa Saleh <smostafa@...gle.com>
> 
> ---
> v3:
> - Set S2S for s2 and not s1 domain
> - Ignore ats check
> 
> v2:
> - Fix index of the STE
> - Fix conflict with ATS
> - Squash the 2 patches and drop enable_nesting
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 5 +----
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 1 +
>  2 files changed, 2 insertions(+), 4 deletions(-)

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

Jason