linux-kernel - Re: [PATCH v3 4/6] iommu/io-pgtable-arm: add support for non-strict mode

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Message-ID: <89cc2201-99ab-3f3b-a2d1-1766515d4375@arm.com>
Date:   Tue, 24 Jul 2018 23:25:14 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Zhen Lei <thunder.leizhen@...wei.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Will Deacon <will.deacon@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/6] iommu/io-pgtable-arm: add support for non-strict
 mode

On 2018-07-12 7:18 AM, Zhen Lei wrote:
> To support the non-strict mode, now we only tlbi and sync for the strict
> mode. But for the non-leaf case, always follow strict mode.
> 
> Use the lowest bit of the iova parameter to pass the strict mode:
> 0, IOMMU_STRICT;
> 1, IOMMU_NON_STRICT;
> Treat 0 as IOMMU_STRICT, so that the unmap operation can compatible with
> other IOMMUs which still use strict mode.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> ---
>   drivers/iommu/io-pgtable-arm.c | 23 ++++++++++++++---------
>   1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index 010a254..9234db3 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -292,7 +292,7 @@ static void __arm_lpae_set_pte(arm_lpae_iopte *ptep, arm_lpae_iopte pte,
>   
>   static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>   			       unsigned long iova, size_t size, int lvl,
> -			       arm_lpae_iopte *ptep);
> +			       arm_lpae_iopte *ptep, int strict);
>   
>   static void __arm_lpae_init_pte(struct arm_lpae_io_pgtable *data,
>   				phys_addr_t paddr, arm_lpae_iopte prot,
> @@ -334,7 +334,7 @@ static int arm_lpae_init_pte(struct arm_lpae_io_pgtable *data,
>   		size_t sz = ARM_LPAE_BLOCK_SIZE(lvl, data);
>   
>   		tblp = ptep - ARM_LPAE_LVL_IDX(iova, lvl, data);
> -		if (WARN_ON(__arm_lpae_unmap(data, iova, sz, lvl, tblp) != sz))
> +		if (WARN_ON(__arm_lpae_unmap(data, iova, sz, lvl, tblp, IOMMU_STRICT) != sz))
>   			return -EINVAL;
>   	}
>   
> @@ -531,7 +531,7 @@ static void arm_lpae_free_pgtable(struct io_pgtable *iop)
>   static size_t arm_lpae_split_blk_unmap(struct arm_lpae_io_pgtable *data,
>   				       unsigned long iova, size_t size,
>   				       arm_lpae_iopte blk_pte, int lvl,
> -				       arm_lpae_iopte *ptep)
> +				       arm_lpae_iopte *ptep, int strict)

DMA code should never ever be splitting blocks anyway, and frankly the 
TLB maintenance here is dodgy enough (since we can't reasonably do 
break-before make as VMSA says we should) that I *really* don't want to 
introduce any possibility of making it more asynchronous. I'd much 
rather just hard-code the expectation of strict == true for this.

Robin.

>   {
>   	struct io_pgtable_cfg *cfg = &data->iop.cfg;
>   	arm_lpae_iopte pte, *tablep;
> @@ -576,15 +576,18 @@ static size_t arm_lpae_split_blk_unmap(struct arm_lpae_io_pgtable *data,
>   	}
>   
>   	if (unmap_idx < 0)
> -		return __arm_lpae_unmap(data, iova, size, lvl, tablep);
> +		return __arm_lpae_unmap(data, iova, size, lvl, tablep, strict);
>   
>   	io_pgtable_tlb_add_flush(&data->iop, iova, size, size, true);
> +	if (!strict)
> +		io_pgtable_tlb_sync(&data->iop);
> +
>   	return size;
>   }
>   
>   static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>   			       unsigned long iova, size_t size, int lvl,
> -			       arm_lpae_iopte *ptep)
> +			       arm_lpae_iopte *ptep, int strict)
>   {
>   	arm_lpae_iopte pte;
>   	struct io_pgtable *iop = &data->iop;
> @@ -609,7 +612,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>   			io_pgtable_tlb_sync(iop);
>   			ptep = iopte_deref(pte, data);
>   			__arm_lpae_free_pgtable(data, lvl + 1, ptep);
> -		} else {
> +		} else if (strict) {
>   			io_pgtable_tlb_add_flush(iop, iova, size, size, true);
>   		}
>   
> @@ -620,25 +623,27 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>   		 * minus the part we want to unmap
>   		 */
>   		return arm_lpae_split_blk_unmap(data, iova, size, pte,
> -						lvl + 1, ptep);
> +						lvl + 1, ptep, strict);
>   	}
>   
>   	/* Keep on walkin' */
>   	ptep = iopte_deref(pte, data);
> -	return __arm_lpae_unmap(data, iova, size, lvl + 1, ptep);
> +	return __arm_lpae_unmap(data, iova, size, lvl + 1, ptep, strict);
>   }
>   
>   static size_t arm_lpae_unmap(struct io_pgtable_ops *ops, unsigned long iova,
>   			     size_t size)
>   {
> +	int strict = ((iova & IOMMU_STRICT_MODE_MASK) == IOMMU_STRICT);
>   	struct arm_lpae_io_pgtable *data = io_pgtable_ops_to_data(ops);
>   	arm_lpae_iopte *ptep = data->pgd;
>   	int lvl = ARM_LPAE_START_LVL(data);
>   
> +	iova &= ~IOMMU_STRICT_MODE_MASK;
>   	if (WARN_ON(iova >= (1ULL << data->iop.cfg.ias)))
>   		return 0;
>   
> -	return __arm_lpae_unmap(data, iova, size, lvl, ptep);
> +	return __arm_lpae_unmap(data, iova, size, lvl, ptep, strict);
>   }
>   
>   static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
>