Re: [RFC PATCH] drivers: iommu: reset cached node if dma_mask is changed

[Joerg Roedel <joro@8bytes.org>]

Adding Robin.

On Tue, May 05, 2020 at 12:07:59AM +0530, Ajay Kumar wrote:
> The current IOVA allocation code stores a cached copy of the
> first allocated IOVA address node, and all the subsequent allocations
> have no way to get past(higher than) the first allocated IOVA range.
> 
> This causes issue when dma_mask for the master device is changed.
> Though the DMA window is increased, the allocation code unaware of
> the change, goes ahead allocating IOVA address lower than the
> first allocated IOVA address.
> 
> This patch adds a check for dma_mask change in the IOVA allocation
> function and resets the cached IOVA node to anchor node everytime
> the dma_mask change is observed.
> 
> NOTE:
>  This patch is needed to address the issue discussed in below thread:
>  https://www.spinics.net/lists/iommu/msg43586.html
> 
> Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
> Signed-off-by: Sathyam Panda <sathya.panda@samsung.com>
> ---
>  drivers/iommu/iova.c | 17 ++++++++++++++++-
>  include/linux/iova.h |  1 +
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index 41c605b0058f..0e99975036ae 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -44,6 +44,7 @@ init_iova_domain(struct iova_domain *iovad, unsigned long granule,
>  	iovad->granule = granule;
>  	iovad->start_pfn = start_pfn;
>  	iovad->dma_32bit_pfn = 1UL << (32 - iova_shift(iovad));
> +	iovad->curr_limit_pfn = iovad->dma_32bit_pfn;
>  	iovad->max32_alloc_size = iovad->dma_32bit_pfn;
>  	iovad->flush_cb = NULL;
>  	iovad->fq = NULL;
> @@ -116,9 +117,20 @@ EXPORT_SYMBOL_GPL(init_iova_flush_queue);
>  static struct rb_node *
>  __get_cached_rbnode(struct iova_domain *iovad, unsigned long limit_pfn)
>  {
> -	if (limit_pfn <= iovad->dma_32bit_pfn)
> +	if (limit_pfn <= iovad->dma_32bit_pfn) {
> +		/* re-init cached node if DMA limit has changed */
> +		if (limit_pfn != iovad->curr_limit_pfn) {
> +			iovad->cached32_node = &iovad->anchor.node;
> +			iovad->curr_limit_pfn = limit_pfn;
> +		}
>  		return iovad->cached32_node;
> +	}
>  
> +	/* re-init cached node if DMA limit has changed */
> +	if (limit_pfn != iovad->curr_limit_pfn) {
> +		iovad->cached_node = &iovad->anchor.node;
> +		iovad->curr_limit_pfn = limit_pfn;
> +	}
>  	return iovad->cached_node;
>  }
>  
> @@ -190,6 +202,9 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
>  	if (size_aligned)
>  		align_mask <<= fls_long(size - 1);
>  
> +	if (limit_pfn != iovad->curr_limit_pfn)
> +		iovad->max32_alloc_size = iovad->dma_32bit_pfn;
> +
>  	/* Walk the tree backwards */
>  	spin_lock_irqsave(&iovad->iova_rbtree_lock, flags);
>  	if (limit_pfn <= iovad->dma_32bit_pfn &&
> diff --git a/include/linux/iova.h b/include/linux/iova.h
> index a0637abffee8..be2220c096ef 100644
> --- a/include/linux/iova.h
> +++ b/include/linux/iova.h
> @@ -73,6 +73,7 @@ struct iova_domain {
>  	unsigned long	granule;	/* pfn granularity for this domain */
>  	unsigned long	start_pfn;	/* Lower limit for this domain */
>  	unsigned long	dma_32bit_pfn;
> +	unsigned long	curr_limit_pfn;	/* Current max limit for this domain */
>  	unsigned long	max32_alloc_size; /* Size of last failed allocation */
>  	struct iova_fq __percpu *fq;	/* Flush Queue */
>  
> -- 
> 2.17.1