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

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Message-ID: <ZtHznQwkJmugKef2@Asurada-Nvidia>
Date: Fri, 30 Aug 2024 09:30:21 -0700
From: Nicolin Chen <nicolinc@...dia.com>
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>,
	<jgg@...pe.ca>, <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.

If I read the SteIllegal() correctly, it seems S2S would conflict
against the STE.EATS settings?

// Check ATS configuration
if ((sec_sid == SS_NonSecure && SMMU_IDR0.ATS == '1') ||
    (sec_sid == SS_Realm && SMMU_R_IDR0.ATS == '1')) &&
    STE.Config != 'x00' then
    // Needs to be NS/Realm, ATS enabled, and not Bypass
        if STE.EATS == '01' && STE.S2S == '1' then
            // Full ATS mode
            if STE.Config == '11x' || constr_unpred_EATS_S2S then
                // if stage 2 enabled or CONSTRAINED UNPREDICTABLE for SMMUv3.0
                return TRUE;
	
So, if master->stall_enabled and master->ats_enabled, there would
be a bad STE?

Thanks
Nicolin