linux-kernel - Re: [PATCH v4 2/5] dma-iommu: Add iommu_dma_opt_mapping

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Message-ID: <06ece223-c71e-baf8-e35e-dbc22a9cf9da@arm.com>
Date:   Tue, 28 Jun 2022 11:56:46 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     John Garry <john.garry@...wei.com>,
        damien.lemoal@...nsource.wdc.com, joro@...tes.org, will@...nel.org,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, hch@....de,
        m.szyprowski@...sung.com
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ide@...r.kernel.org, iommu@...ts.linux-foundation.org,
        iommu@...ts.linux.dev, linux-scsi@...r.kernel.org,
        linuxarm@...wei.com
Subject: Re: [PATCH v4 2/5] dma-iommu: Add iommu_dma_opt_mapping_size()

On 2022-06-27 16:25, John Garry wrote:
> Add the IOMMU callback for DMA mapping API dma_opt_mapping_size(), which
> allows the drivers to know the optimal mapping limit and thus limit the
> requested IOVA lengths.
> 
> This value is based on the IOVA rcache range limit, as IOVAs allocated
> above this limit must always be newly allocated, which may be quite slow.

Acked-by: Robin Murphy <robin.murphy@....com>

> Signed-off-by: John Garry <john.garry@...wei.com>
> Reviewed-by: Damien Le Moal <damien.lemoal@...nsource.wdc.com>
> ---
>   drivers/iommu/dma-iommu.c | 6 ++++++
>   drivers/iommu/iova.c      | 5 +++++
>   include/linux/iova.h      | 2 ++
>   3 files changed, 13 insertions(+)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index f90251572a5d..9e1586447ee8 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1459,6 +1459,11 @@ static unsigned long iommu_dma_get_merge_boundary(struct device *dev)
>   	return (1UL << __ffs(domain->pgsize_bitmap)) - 1;
>   }
>   
> +static size_t iommu_dma_opt_mapping_size(void)
> +{
> +	return iova_rcache_range();
> +}
> +
>   static const struct dma_map_ops iommu_dma_ops = {
>   	.alloc			= iommu_dma_alloc,
>   	.free			= iommu_dma_free,
> @@ -1479,6 +1484,7 @@ static const struct dma_map_ops iommu_dma_ops = {
>   	.map_resource		= iommu_dma_map_resource,
>   	.unmap_resource		= iommu_dma_unmap_resource,
>   	.get_merge_boundary	= iommu_dma_get_merge_boundary,
> +	.opt_mapping_size	= iommu_dma_opt_mapping_size,
>   };
>   
>   /*
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index db77aa675145..9f00b58d546e 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -26,6 +26,11 @@ static unsigned long iova_rcache_get(struct iova_domain *iovad,
>   static void free_cpu_cached_iovas(unsigned int cpu, struct iova_domain *iovad);
>   static void free_iova_rcaches(struct iova_domain *iovad);
>   
> +unsigned long iova_rcache_range(void)
> +{
> +	return PAGE_SIZE << (IOVA_RANGE_CACHE_MAX_SIZE - 1);
> +}
> +
>   static int iova_cpuhp_dead(unsigned int cpu, struct hlist_node *node)
>   {
>   	struct iova_domain *iovad;
> diff --git a/include/linux/iova.h b/include/linux/iova.h
> index 320a70e40233..c6ba6d95d79c 100644
> --- a/include/linux/iova.h
> +++ b/include/linux/iova.h
> @@ -79,6 +79,8 @@ static inline unsigned long iova_pfn(struct iova_domain *iovad, dma_addr_t iova)
>   int iova_cache_get(void);
>   void iova_cache_put(void);
>   
> +unsigned long iova_rcache_range(void);
> +
>   void free_iova(struct iova_domain *iovad, unsigned long pfn);
>   void __free_iova(struct iova_domain *iovad, struct iova *iova);
>   struct iova *alloc_iova(struct iova_domain *iovad, unsigned long size,