Re: [PATCH v2] iommu/iova: Reset max32_alloc_size after cleaning rcache in the fail path

[Robin Murphy]

On 2022-03-01 01:59, yf.wang--- via iommu wrote:
> From: Yunfei Wang <yf.wang@xxxxxxxxxxxx>
>
> In alloc_iova_fast function, if __alloc_and_insert_iova_range fail,
> alloc_iova_fast will try flushing rcache and retry alloc iova, but
> this has an issue:
>
> Since __alloc_and_insert_iova_range fail will set the current alloc
> iova size to max32_alloc_size (iovad->max32_alloc_size = size),
> when the retry is executed into the __alloc_and_insert_iova_range
> function, the retry action will be blocked by the check condition
> (size >= iovad->max32_alloc_size) and goto iova32_full directly,
> causes the action of retry regular alloc iova in
> __alloc_and_insert_iova_range to not actually be executed.
>
> Based on the above, so need reset max32_alloc_size before retry alloc
> iova when alloc iova fail, that is set the initial dma_32bit_pfn value
> of iovad to max32_alloc_size, so that the action of retry alloc iova
> in __alloc_and_insert_iova_range can be executed.

Have you observed this making any difference in practice?

Given that both free_cpu_cached_iovas() and free_global_cached_iovas() 
call iova_magazine_free_pfns(), which calls remove_iova(), which calls 
__cached_rbnode_delete_update(), I'm thinking no...

Robin.

> Signed-off-by: Yunfei Wang <yf.wang@xxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.*
> ---
> v2: Cc stable@xxxxxxxxxxxxxxx
>      1. This patch needs to be merged stable branch, add stable@xxxxxxxxxxxxxxx
>         in mail list.
>
> ---
>   drivers/iommu/iova.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index b28c9435b898..0c085ae8293f 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -453,6 +453,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size,
>   retry:
>   	new_iova = alloc_iova(iovad, size, limit_pfn, true);
>   	if (!new_iova) {
> +		unsigned long flags;
>   		unsigned int cpu;
>   
>   		if (!flush_rcache)
> @@ -463,6 +464,12 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size,
>   		for_each_online_cpu(cpu)
>   			free_cpu_cached_iovas(cpu, iovad);
>   		free_global_cached_iovas(iovad);
> +
> +		/* Reset max32_alloc_size after flushing rcache for retry */
> +		spin_lock_irqsave(&iovad->iova_rbtree_lock, flags);
> +		iovad->max32_alloc_size = iovad->dma_32bit_pfn;
> +		spin_unlock_irqrestore(&iovad->iova_rbtree_lock, flags);
> +
>   		goto retry;
>   	}
>   
>
>
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