linux-kernel - Re: [PATCH v3 2/6] iommu/dma: add support for non-strict mode

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Message-ID: <4a668c7c-bce6-eef0-e11d-319333c60fcb@arm.com>
Date:   Tue, 24 Jul 2018 23:01:58 +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 2/6] iommu/dma: add support for non-strict mode

On 2018-07-12 7:18 AM, Zhen Lei wrote:
> 1. Save the related domain pointer in struct iommu_dma_cookie, make iovad
>     capable call domain->ops->flush_iotlb_all to flush TLB.
> 2. Add a new iommu capability: IOMMU_CAP_NON_STRICT, which used to indicate
>     that the iommu domain support non-strict mode.
> 3. During the iommu domain initialization phase, call capable() to check
>     whether it support non-strcit mode. If so, call init_iova_flush_queue
>     to register iovad->flush_cb callback.
> 4. All unmap(contains iova-free) APIs will finally invoke __iommu_dma_unmap
>     -->iommu_dma_free_iova. If the domain is non-strict, call queue_iova to
>     put off iova freeing.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> ---
>   drivers/iommu/dma-iommu.c | 25 +++++++++++++++++++++++++
>   include/linux/iommu.h     |  7 +++++++
>   2 files changed, 32 insertions(+)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index ddcbbdb..9f0c77a 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -55,6 +55,7 @@ struct iommu_dma_cookie {
>   	};
>   	struct list_head		msi_page_list;
>   	spinlock_t			msi_lock;
> +	struct iommu_domain		*domain_non_strict;
>   };
>   
>   static inline size_t cookie_msi_granule(struct iommu_dma_cookie *cookie)
> @@ -257,6 +258,17 @@ static int iova_reserve_iommu_regions(struct device *dev,
>   	return ret;
>   }
>   
> +static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
> +{
> +	struct iommu_dma_cookie *cookie;
> +	struct iommu_domain *domain;
> +
> +	cookie = container_of(iovad, struct iommu_dma_cookie, iovad);
> +	domain = cookie->domain_non_strict;
> +
> +	domain->ops->flush_iotlb_all(domain);
> +}
> +
>   /**
>    * iommu_dma_init_domain - Initialise a DMA mapping domain
>    * @domain: IOMMU domain previously prepared by iommu_get_dma_cookie()
> @@ -272,6 +284,7 @@ static int iova_reserve_iommu_regions(struct device *dev,
>   int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
>   		u64 size, struct device *dev)
>   {
> +	const struct iommu_ops *ops = domain->ops;
>   	struct iommu_dma_cookie *cookie = domain->iova_cookie;
>   	struct iova_domain *iovad = &cookie->iovad;
>   	unsigned long order, base_pfn, end_pfn;
> @@ -308,6 +321,15 @@ int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
>   	}
>   
>   	init_iova_domain(iovad, 1UL << order, base_pfn);
> +
> +	if ((ops->capable && ops->capable(IOMMU_CAP_NON_STRICT)) &&
> +	    (IOMMU_DOMAIN_STRICT_MODE(domain) == IOMMU_NON_STRICT)) {
> +		BUG_ON(!ops->flush_iotlb_all);
> +
> +		cookie->domain_non_strict = domain;
> +		init_iova_flush_queue(iovad, iommu_dma_flush_iotlb_all, NULL);
> +	}
> +
>   	if (!dev)
>   		return 0;
>   
> @@ -390,6 +412,9 @@ static void iommu_dma_free_iova(struct iommu_dma_cookie *cookie,
>   	/* The MSI case is only ever cleaning up its most recent allocation */
>   	if (cookie->type == IOMMU_DMA_MSI_COOKIE)
>   		cookie->msi_iova -= size;
> +	else if (cookie->domain_non_strict)
> +		queue_iova(iovad, iova_pfn(iovad, iova),
> +				size >> iova_shift(iovad), 0);
>   	else
>   		free_iova_fast(iovad, iova_pfn(iovad, iova),
>   				size >> iova_shift(iovad));
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 19938ee..82ed979 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -86,6 +86,12 @@ struct iommu_domain_geometry {
>   #define IOMMU_DOMAIN_DMA	(__IOMMU_DOMAIN_PAGING |	\
>   				 __IOMMU_DOMAIN_DMA_API)
>   
> +#define IOMMU_STRICT		0
> +#define IOMMU_NON_STRICT	1
> +#define IOMMU_STRICT_MODE_MASK	1UL
> +#define IOMMU_DOMAIN_STRICT_MODE(domain)	\
> +		(domain->type != IOMMU_DOMAIN_UNMANAGED)
> +
>   struct iommu_domain {
>   	unsigned type;
>   	const struct iommu_ops *ops;
> @@ -101,6 +107,7 @@ enum iommu_cap {
>   					   transactions */
>   	IOMMU_CAP_INTR_REMAP,		/* IOMMU supports interrupt isolation */
>   	IOMMU_CAP_NOEXEC,		/* IOMMU_NOEXEC flag */
> +	IOMMU_CAP_NON_STRICT,		/* IOMMU supports non-strict mode */

This still isn't a capability of the hardware. Non-strict mode is pure 
software policy; *every IOMMU ever* supports it.

If you want to have this kind of per-driver control, make it a domain 
attribute - that's not only more logical, but should also work out a lot 
cleaner overall.

Robin.

>   };
>   
>   /*
>