RE: [PATCH v10 10/13] iommu/arm-smmu-v3: Check for SVA features

Shameerali Kolothum Thodi
2020-09-21T09:01:15Z

Hi Jean,

> -----Original Message-----
> From: iommu [mailto:iommu-bounces@lists.linux-foundation.org] On Behalf Of
> Jean-Philippe Brucker
> Sent: 18 September 2020 11:19
> To: iommu@lists.linux-foundation.org; linux-arm-kernel@lists.infradead.org;
> linux-mm@kvack.org
> Cc: fenghua.yu@intel.com; Jean-Philippe Brucker <jean-philippe@linaro.org>;
> catalin.marinas@arm.com; Suzuki K Poulose <suzuki.poulose@arm.com>;
> robin.murphy@arm.com; zhangfei.gao@linaro.org; will@kernel.org
> Subject: [PATCH v10 10/13] iommu/arm-smmu-v3: Check for SVA features
>
> Aggregate all sanity-checks for sharing CPU page tables with the SMMU
> under a single ARM_SMMU_FEAT_SVA bit. For PCIe SVA, users also need to
> check FEAT_ATS and FEAT_PRI. For platform SVA, they will have to check
> FEAT_STALLS.
>
> Introduce ARM_SMMU_FEAT_BTM (Broadcast TLB Maintenance), but don't
> enable it at the moment. Since the entire VMID space is shared with the
> CPU, enabling DVM (by clearing SMMU_CR2.PTM) could result in
> over-invalidation and affect performance of stage-2 mappings.
>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
> v10:
> * Check that 52-bit VA is supported on the SMMU side if vabits_actual
> requires it.
> * Check arm64_kernel_unmapped_at_el0() instead of
> CONFIG_UNMAP_KERNEL_AT_EL0
> ---
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 10 +++++
> .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 45
> +++++++++++++++++++
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 3 ++
> 3 files changed, 58 insertions(+)
>
> 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 90c08f156b43..7b14b48a26c7 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> @@ -602,6 +602,8 @@ struct arm_smmu_device {
> #define ARM_SMMU_FEAT_STALL_FORCE (1 << 13)
> #define ARM_SMMU_FEAT_VAX (1 << 14)
> #define ARM_SMMU_FEAT_RANGE_INV (1 << 15)
> +#define ARM_SMMU_FEAT_BTM (1 << 16)
> +#define ARM_SMMU_FEAT_SVA (1 << 17)
> u32 features;
>
> #define ARM_SMMU_OPT_SKIP_PREFETCH (1 << 0)
> @@ -683,4 +685,12 @@ int arm_smmu_write_ctx_desc(struct
> arm_smmu_domain *smmu_domain, int ssid,
> void arm_smmu_tlb_inv_asid(struct arm_smmu_device *smmu, u16 asid);
> bool arm_smmu_free_asid(struct arm_smmu_ctx_desc *cd);
>
> +#ifdef CONFIG_ARM_SMMU_V3_SVA
> +bool arm_smmu_sva_supported(struct arm_smmu_device *smmu);
> +#else /* CONFIG_ARM_SMMU_V3_SVA */
> +static inline bool arm_smmu_sva_supported(struct arm_smmu_device
> *smmu)
> +{
> + return false;
> +}
> +#endif /* CONFIG_ARM_SMMU_V3_SVA */
> #endif /* _ARM_SMMU_V3_H */
> 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 ef3fcfa72187..cb94c0924196 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
> @@ -152,3 +152,48 @@ static void arm_smmu_free_shared_cd(struct
> arm_smmu_ctx_desc *cd)
> kfree(cd);
> }
> }
> +
> +bool arm_smmu_sva_supported(struct arm_smmu_device *smmu)
> +{
> + unsigned long reg, fld;
> + unsigned long oas;
> + unsigned long asid_bits;
> + u32 feat_mask = ARM_SMMU_FEAT_BTM |
> ARM_SMMU_FEAT_COHERENCY;

Why is BTM mandated for SVA? I couldn't find this requirement in SMMU spec
(Sorry if I missed it or this got discussed earlier). But if performance is the only concern here,
is it better just to allow it with a warning rather than limiting SMMUs without BTM?

Thanks,
Shameer

> +
> + if (vabits_actual == 52)
> + feat_mask |= ARM_SMMU_FEAT_VAX;
> +
> + if ((smmu->features & feat_mask) != feat_mask)
> + return false;
> +
> + if (!(smmu->pgsize_bitmap & PAGE_SIZE))
> + return false;
> +
> + /*
> + * Get the smallest PA size of all CPUs (sanitized by cpufeature). We're
> + * not even pretending to support AArch32 here. Abort if the MMU
> outputs
> + * addresses larger than what we support.
> + */
> + reg = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1);
> + fld = cpuid_feature_extract_unsigned_field(reg,
> ID_AA64MMFR0_PARANGE_SHIFT);
> + oas = id_aa64mmfr0_parange_to_phys_shift(fld);
> + if (smmu->oas < oas)
> + return false;
> +
> + /* We can support bigger ASIDs than the CPU, but not smaller */
> + fld = cpuid_feature_extract_unsigned_field(reg,
> ID_AA64MMFR0_ASID_SHIFT);
> + asid_bits = fld ? 16 : 8;
> + if (smmu->asid_bits < asid_bits)
> + return false;
> +
> + /*
> + * See max_pinned_asids in arch/arm64/mm/context.c. The following is
> + * generally the maximum number of bindable processes.
> + */
> + if (arm64_kernel_unmapped_at_el0())
> + asid_bits--;
> + dev_dbg(smmu->dev, "%d shared contexts\n", (1 << asid_bits) -
> + num_possible_cpus() - 2);
> +
> + return true;
> +}
> 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 e99ebdd4c841..44c57bcfe112 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -3257,6 +3257,9 @@ static int arm_smmu_device_hw_probe(struct
> arm_smmu_device *smmu)
>
> smmu->ias = max(smmu->ias, smmu->oas);
>
> + if (arm_smmu_sva_supported(smmu))
> + smmu->features |= ARM_SMMU_FEAT_SVA;
> +
> dev_info(smmu->dev, "ias %lu-bit, oas %lu-bit (features 0x%08x)\n",
> smmu->ias, smmu->oas, smmu->features);
> return 0;
> --
> 2.28.0
>
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