Re: [PATCH] iommu/arm-smmu-v2: Workaround for ThunderX errata#27704

[Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>]

On Fri, Feb 05, 2016 at 10:47:07AM -0800, tchalamarla-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org wrote:
> From: Tirumalesh Chalamarla <tchalamarla-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org>
> 
> An issue exists whereby the Linux kernel requires that ASIDs are a
> unique namespace per SMMU.  

The SMMU architecture requires this, and Linux relies on hardware
following the architecture.

Please describe the problem correctly. i.e. that the hardware
erroneously shares TLBs between SMMU instances.

> That ASID-local choice conflicts with the
> CN88xx SMMU, where only shared ASID namespaces are supported;
> specifically within a given node SMMU0 and SMMU1 share, as does SMMU2
> and SMMU3. CN88xx SMMU also requires global VMIDs.
> 
> This patch tries to address these issuee by supplying asid and vmid
> transformations from devicetree.
> 
> Signed-off-by: Akula Geethasowjanya <Geethasowjanya.Akula-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org>
> Signed-off-by: Tirumalesh Chalamarla <tchalamarla-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org>
> ---
>  .../devicetree/bindings/iommu/arm,smmu.txt         | 16 ++++++
>  drivers/iommu/arm-smmu.c                           | 59 ++++++++++++++++++----
>  2 files changed, 65 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.txt b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> index 7180745..eef06d0 100644
> --- a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> +++ b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> @@ -55,6 +55,22 @@ conditions.
>                    aliases of secure registers have to be used during
>                    SMMU configuration.
>  
> +- thunderx,smmu-asid-transform	: Enable proper handling for buggy
> +		  implementations that require special transformations
> +		  for smmu asid. if this property exists asid-transform
> +		  property must be present.
> +
> +- thunderx,smmu-vmid-transform	: Enable proper handling for buggy
> +		  implementations that require special transformations
> +		  for smmu vmid. if this property exists vmid-transform
> +		  property must be present.
> +
> +- asid-transform 	: Transform mask that needs to be applied to asid.
> +			This property has to be specified as '/bits/ 8' value.
> +
> +- vmid-transform 	: Transform mask that needs to be applied to vmid.
> +			This property has to be specified as '/bits/ 8' value.

Don't bother with /bits/ 8. It saves no space in the DTB and only adds
to confusion. Use a full cell, and of_property_read_u32, and validate
that the value is in range.

Having two properties for each seems redundant. The presence of a mask
should be sufficient to make it clear that the use of the mask is
required.

These properties aren't sufficiently described. How is the mask
"applied", and what is it applied to? What constraints does it impose
on the OS's selection of ASIDs/VMIDs?

>From the looks of the patch, it's ANDed into the value Linux has
selected, so it sounds like an OS must avoid using any bits set in any
mask on any SMMU instance. That sounds very difficult to ensure in
general, and very fragile.

Mark.

> +
>  Example:
>  
>          smmu {
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 59ee4b8..8047834 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -300,8 +300,12 @@ struct arm_smmu_device {
>  	u32				features;
>  
>  #define ARM_SMMU_OPT_SECURE_CFG_ACCESS (1 << 0)
> +#define ARM_SMMU_OPT_TRANSFORM_ASID	(1 << 1)
> +#define ARM_SMMU_OPT_TRANSFORM_VMID	(1 << 2)
>  	u32				options;
>  	enum arm_smmu_arch_version	version;
> +	u8				asid_transform;
> +	u8				vmid_transform;
>  
>  	u32				num_context_banks;
>  	u32				num_s2_context_banks;
> @@ -330,8 +334,25 @@ struct arm_smmu_cfg {
>  };
>  #define INVALID_IRPTNDX			0xff
>  
> -#define ARM_SMMU_CB_ASID(cfg)		((cfg)->cbndx)
> -#define ARM_SMMU_CB_VMID(cfg)		((cfg)->cbndx + 1)
> +/*
> + * ThunderX has a unique requirement because of ERRATA#27704
> + * An issue exists whereby the Linux kernel requires that ASIDs are a
> + * unique namespace per SMMU.  That ASID-local choice conflicts with the
> + * CN88xx SMMU, where only shared ASID namespaces are supported;
> + * specifically within a given node SMMU0 and SMMU1 share, as does SMMU2
> + * and SMMU3.
> + * CN88xx SMMU also requires global VMIDs.
> + */
> +
> +#define ARM_SMMU_CB_ASID(smmu, cfg)					\
> +		(((smmu)->options & ARM_SMMU_OPT_TRANSFORM_ASID)	\
> +		? ((cfg)->cbndx | (smmu)->asid_transform)		\
> +		: ((cfg)->cbndx))
> +
> +#define ARM_SMMU_CB_VMID(smmu, cfg)					\
> +		(((smmu)->options & ARM_SMMU_OPT_TRANSFORM_VMID)	\
> +		? (((cfg)->cbndx + 1) | (smmu)->vmid_transform)		\
> +		: ((cfg)->cbndx + 1))
>  
>  enum arm_smmu_domain_stage {
>  	ARM_SMMU_DOMAIN_S1 = 0,
> @@ -361,6 +382,8 @@ struct arm_smmu_option_prop {
>  
>  static struct arm_smmu_option_prop arm_smmu_options[] = {
>  	{ ARM_SMMU_OPT_SECURE_CFG_ACCESS, "calxeda,smmu-secure-config-access" },
> +	{ ARM_SMMU_OPT_TRANSFORM_ASID, "thunderx,smmu-asid-transform" },
> +	{ ARM_SMMU_OPT_TRANSFORM_VMID, "thunderx,smmu-vmid-transform" },
>  	{ 0, NULL},
>  };
>  
> @@ -570,11 +593,11 @@ static void arm_smmu_tlb_inv_context(void *cookie)
>  
>  	if (stage1) {
>  		base = ARM_SMMU_CB_BASE(smmu) + ARM_SMMU_CB(smmu, cfg->cbndx);
> -		writel_relaxed(ARM_SMMU_CB_ASID(cfg),
> +		writel_relaxed(ARM_SMMU_CB_ASID(smmu, cfg),
>  			       base + ARM_SMMU_CB_S1_TLBIASID);
>  	} else {
>  		base = ARM_SMMU_GR0(smmu);
> -		writel_relaxed(ARM_SMMU_CB_VMID(cfg),
> +		writel_relaxed(ARM_SMMU_CB_VMID(smmu, cfg),
>  			       base + ARM_SMMU_GR0_TLBIVMID);
>  	}
>  
> @@ -596,7 +619,7 @@ static void arm_smmu_tlb_inv_range_nosync(unsigned long iova, size_t size,
>  
>  		if (!IS_ENABLED(CONFIG_64BIT) || smmu->version == ARM_SMMU_V1) {
>  			iova &= ~12UL;
> -			iova |= ARM_SMMU_CB_ASID(cfg);
> +			iova |= ARM_SMMU_CB_ASID(smmu, cfg);
>  			do {
>  				writel_relaxed(iova, reg);
>  				iova += granule;
> @@ -604,7 +627,7 @@ static void arm_smmu_tlb_inv_range_nosync(unsigned long iova, size_t size,
>  #ifdef CONFIG_64BIT
>  		} else {
>  			iova >>= 12;
> -			iova |= (u64)ARM_SMMU_CB_ASID(cfg) << 48;
> +			iova |= (u64)ARM_SMMU_CB_ASID(smmu, cfg) << 48;
>  			do {
>  				writeq_relaxed(iova, reg);
>  				iova += granule >> 12;
> @@ -624,7 +647,7 @@ static void arm_smmu_tlb_inv_range_nosync(unsigned long iova, size_t size,
>  #endif
>  	} else {
>  		reg = ARM_SMMU_GR0(smmu) + ARM_SMMU_GR0_TLBIVMID;
> -		writel_relaxed(ARM_SMMU_CB_VMID(cfg), reg);
> +		writel_relaxed(ARM_SMMU_CB_VMID(smmu, cfg), reg);
>  	}
>  }
>  
> @@ -752,7 +775,7 @@ static void arm_smmu_init_context_bank(struct arm_smmu_domain *smmu_domain,
>  		reg |= (CBAR_S1_BPSHCFG_NSH << CBAR_S1_BPSHCFG_SHIFT) |
>  			(CBAR_S1_MEMATTR_WB << CBAR_S1_MEMATTR_SHIFT);
>  	} else {
> -		reg |= ARM_SMMU_CB_VMID(cfg) << CBAR_VMID_SHIFT;
> +		reg |= ARM_SMMU_CB_VMID(smmu, cfg) << CBAR_VMID_SHIFT;
>  	}
>  	writel_relaxed(reg, gr1_base + ARM_SMMU_GR1_CBAR(cfg->cbndx));
>  
> @@ -760,11 +783,11 @@ static void arm_smmu_init_context_bank(struct arm_smmu_domain *smmu_domain,
>  	if (stage1) {
>  		reg64 = pgtbl_cfg->arm_lpae_s1_cfg.ttbr[0];
>  
> -		reg64 |= ((u64)ARM_SMMU_CB_ASID(cfg)) << TTBRn_ASID_SHIFT;
> +		reg64 |= ((u64)ARM_SMMU_CB_ASID(smmu, cfg)) << TTBRn_ASID_SHIFT;
>  		smmu_writeq(reg64, cb_base + ARM_SMMU_CB_TTBR0);
>  
>  		reg64 = pgtbl_cfg->arm_lpae_s1_cfg.ttbr[1];
> -		reg64 |= ((u64)ARM_SMMU_CB_ASID(cfg)) << TTBRn_ASID_SHIFT;
> +		reg64 |= ((u64)ARM_SMMU_CB_ASID(smmu, cfg)) << TTBRn_ASID_SHIFT;
>  		smmu_writeq(reg64, cb_base + ARM_SMMU_CB_TTBR1);
>  	} else {
>  		reg64 = pgtbl_cfg->arm_lpae_s2_cfg.vttbr;
> @@ -1793,6 +1816,22 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
>  
>  	parse_driver_options(smmu);
>  
> +	if (smmu->options & ARM_SMMU_OPT_TRANSFORM_ASID) {
> +		if (of_property_read_u8(dev->of_node, "#asid-transform",
> +					 &smmu->asid_transform)) {
> +			dev_err(dev, "missing #asid-transform property\n");
> +			return -ENODEV;
> +		}
> +	}
> +
> +	if (smmu->options & ARM_SMMU_OPT_TRANSFORM_VMID) {
> +		if (of_property_read_u8(dev->of_node, "#vmid-transform",
> +					 &smmu->vmid_transform)) {
> +			dev_err(dev, "missing #vmid-transform property\n");
> +			return -ENODEV;
> +		}
> +	}
> +
`  	if (smmu->version > ARM_SMMU_V1 &&
>  	    smmu->num_context_banks != smmu->num_context_irqs) {
>  		dev_err(dev,
> -- 
> 2.1.0
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>