Re: [PATCH v7 18/24] iommu/arm-smmu-v3: Add support for Hardware Translation Table Update

[Xiang Zheng <zhengxiang9@huawei.com>]

Hi Jean,

This patch only enables HTTU bits in CDs. Is it also neccessary to enable
HTTU bits in STEs in this patch?

On 2020/5/20 1:54, Jean-Philippe Brucker wrote:
> If the SMMU supports it and the kernel was built with HTTU support,
> enable hardware update of access and dirty flags. This is essential for
> shared page tables, to reduce the number of access faults on the fault
> queue. Normal DMA with io-pgtables doesn't currently use the access or
> dirty flags.
> 
> We can enable HTTU even if CPUs don't support it, because the kernel
> always checks for HW dirty bit and updates the PTE flags atomically.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
>  drivers/iommu/arm-smmu-v3.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 1386d4d2bc60..6a368218f54c 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -58,6 +58,8 @@
>  #define IDR0_ASID16			(1 << 12)
>  #define IDR0_ATS			(1 << 10)
>  #define IDR0_HYP			(1 << 9)
> +#define IDR0_HD				(1 << 7)
> +#define IDR0_HA				(1 << 6)
>  #define IDR0_BTM			(1 << 5)
>  #define IDR0_COHACC			(1 << 4)
>  #define IDR0_TTF			GENMASK(3, 2)
> @@ -311,6 +313,9 @@
>  #define CTXDESC_CD_0_TCR_IPS		GENMASK_ULL(34, 32)
>  #define CTXDESC_CD_0_TCR_TBI0		(1ULL << 38)
>  
> +#define CTXDESC_CD_0_TCR_HA		(1UL << 43)
> +#define CTXDESC_CD_0_TCR_HD		(1UL << 42)
> +

>  #define CTXDESC_CD_0_AA64		(1UL << 41)
>  #define CTXDESC_CD_0_S			(1UL << 44)
>  #define CTXDESC_CD_0_R			(1UL << 45)
> @@ -663,6 +668,8 @@ struct arm_smmu_device {
>  #define ARM_SMMU_FEAT_E2H		(1 << 16)
>  #define ARM_SMMU_FEAT_BTM		(1 << 17)
>  #define ARM_SMMU_FEAT_SVA		(1 << 18)
> +#define ARM_SMMU_FEAT_HA		(1 << 19)
> +#define ARM_SMMU_FEAT_HD		(1 << 20)
>  	u32				features;
>  
>  #define ARM_SMMU_OPT_SKIP_PREFETCH	(1 << 0)
> @@ -1718,10 +1725,17 @@ static int arm_smmu_write_ctx_desc(struct arm_smmu_domain *smmu_domain,
>  		 * this substream's traffic
>  		 */
>  	} else { /* (1) and (2) */
> +		u64 tcr = cd->tcr;
> +
>  		cdptr[1] = cpu_to_le64(cd->ttbr & CTXDESC_CD_1_TTB0_MASK);
>  		cdptr[2] = 0;
>  		cdptr[3] = cpu_to_le64(cd->mair);
>  
> +		if (!(smmu->features & ARM_SMMU_FEAT_HD))
> +			tcr &= ~CTXDESC_CD_0_TCR_HD;
> +		if (!(smmu->features & ARM_SMMU_FEAT_HA))
> +			tcr &= ~CTXDESC_CD_0_TCR_HA;
> +
>  		/*
>  		 * STE is live, and the SMMU might read dwords of this CD in any
>  		 * order. Ensure that it observes valid values before reading
> @@ -1729,7 +1743,7 @@ static int arm_smmu_write_ctx_desc(struct arm_smmu_domain *smmu_domain,
>  		 */
>  		arm_smmu_sync_cd(smmu_domain, ssid, true);
>  
> -		val = cd->tcr |
> +		val = tcr |
>  #ifdef __BIG_ENDIAN
>  			CTXDESC_CD_0_ENDI |
>  #endif
> @@ -1958,10 +1972,12 @@ static struct arm_smmu_ctx_desc *arm_smmu_alloc_shared_cd(struct mm_struct *mm)
>  		return old_cd;
>  	}
>  
> +	/* HA and HD will be filtered out later if not supported by the SMMU */
>  	tcr = FIELD_PREP(CTXDESC_CD_0_TCR_T0SZ, 64ULL - VA_BITS) |
>  	      FIELD_PREP(CTXDESC_CD_0_TCR_IRGN0, ARM_LPAE_TCR_RGN_WBWA) |
>  	      FIELD_PREP(CTXDESC_CD_0_TCR_ORGN0, ARM_LPAE_TCR_RGN_WBWA) |
>  	      FIELD_PREP(CTXDESC_CD_0_TCR_SH0, ARM_LPAE_TCR_SH_IS) |
> +	      CTXDESC_CD_0_TCR_HA | CTXDESC_CD_0_TCR_HD |
>  	      CTXDESC_CD_0_TCR_EPD1 | CTXDESC_CD_0_AA64;
>  
>  	switch (PAGE_SIZE) {
> @@ -4454,6 +4470,12 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
>  			smmu->features |= ARM_SMMU_FEAT_E2H;
>  	}
>  
> +	if (reg & (IDR0_HA | IDR0_HD)) {

> +		smmu->features |= ARM_SMMU_FEAT_HA;
> +		if (reg & IDR0_HD)
> +			smmu->features |= ARM_SMMU_FEAT_HD;
> +	}
> +

>  	/*
>  	 * If the CPU is using VHE, but the SMMU doesn't support it, the SMMU
>  	 * will create TLB entries for NH-EL1 world and will miss the
> 

-- 
Thanks,
Xiang