linux-kernel - Re: [PATCH v3 2/3] iommu/arm: Add BBM Level 2 smmu feature

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Message-ID: <07c36889-10d3-4944-a039-3a30fbdca883@arm.com>
Date: Thu, 13 Mar 2025 16:18:12 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Mikołaj Lenczewski <miko.lenczewski@....com>,
 suzuki.poulose@....com, yang@...amperecomputing.com, corbet@....net,
 catalin.marinas@....com, will@...nel.org, jean-philippe@...aro.org,
 robin.murphy@....com, joro@...tes.org, akpm@...ux-foundation.org,
 mark.rutland@....com, joey.gouly@....com, maz@...nel.org,
 james.morse@....com, broonie@...nel.org, anshuman.khandual@....com,
 oliver.upton@...ux.dev, ioworker0@...il.com, baohua@...nel.org,
 david@...hat.com, jgg@...pe.ca, shameerali.kolothum.thodi@...wei.com,
 nicolinc@...dia.com, mshavit@...gle.com, jsnitsel@...hat.com,
 smostafa@...gle.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 iommu@...ts.linux.dev
Subject: Re: [PATCH v3 2/3] iommu/arm: Add BBM Level 2 smmu feature

On 13/03/2025 10:41, Mikołaj Lenczewski wrote:
> For supporting BBM Level 2 for userspace mappings, we want to ensure
> that the smmu also supports its own version of BBM Level 2. Luckily, the
> smmu spec (IHI 0070G 3.21.1.3) is stricter than the aarch64 spec (DDI
> 0487K.a D8.16.2), so already guarantees that no aborts are raised when
> BBM level 2 is claimed.
> 
> Add the feature and testing for it under arm_smmu_sva_supported().
> 
> Signed-off-by: Mikołaj Lenczewski <miko.lenczewski@....com>

Reviewed-by: Ryan Roberts <ryan.roberts@....com>

> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 3 +++
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c     | 3 +++
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h     | 4 ++++
>  3 files changed, 10 insertions(+)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> index 9ba596430e7c..6ba182572788 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> @@ -222,6 +222,9 @@ bool arm_smmu_sva_supported(struct arm_smmu_device *smmu)
>  		feat_mask |= ARM_SMMU_FEAT_VAX;
>  	}
>  
> +	if (system_supports_bbml2_noabort())
> +		feat_mask |= ARM_SMMU_FEAT_BBML2;
> +
>  	if ((smmu->features & feat_mask) != feat_mask)
>  		return false;
>  
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 358072b4e293..dcee0bdec924 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -4406,6 +4406,9 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
>  	if (FIELD_GET(IDR3_RIL, reg))
>  		smmu->features |= ARM_SMMU_FEAT_RANGE_INV;
>  
> +	if (FIELD_GET(IDR3_BBML, reg) == IDR3_BBML2)
> +		smmu->features |= ARM_SMMU_FEAT_BBML2;
> +
>  	/* IDR5 */
>  	reg = readl_relaxed(smmu->base + ARM_SMMU_IDR5);
>  
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> index bd9d7c85576a..85eaf3ab88c2 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> @@ -60,6 +60,9 @@ struct arm_smmu_device;
>  #define ARM_SMMU_IDR3			0xc
>  #define IDR3_FWB			(1 << 8)
>  #define IDR3_RIL			(1 << 10)
> +#define IDR3_BBML			GENMASK(12, 11)
> +#define IDR3_BBML1			(1 << 11)
> +#define IDR3_BBML2			(2 << 11)
>  
>  #define ARM_SMMU_IDR5			0x14
>  #define IDR5_STALL_MAX			GENMASK(31, 16)
> @@ -754,6 +757,7 @@ struct arm_smmu_device {
>  #define ARM_SMMU_FEAT_HA		(1 << 21)
>  #define ARM_SMMU_FEAT_HD		(1 << 22)
>  #define ARM_SMMU_FEAT_S2FWB		(1 << 23)
> +#define ARM_SMMU_FEAT_BBML2		(1 << 24)
>  	u32				features;
>  
>  #define ARM_SMMU_OPT_SKIP_PREFETCH	(1 << 0)