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

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Message-ID: <b10031aa-8e49-70b3-b498-8aa6b7021fbb@arm.com>
Date:   Tue, 1 Mar 2022 13:56:29 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     yf.wang@...iatek.com
Cc:     wsd_upstream@...iatek.com, linux-kernel@...r.kernel.org,
        Libo.Kang@...iatek.com, iommu@...ts.linux-foundation.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, Ning.Li@...iatek.com,
        matthias.bgg@...il.com, stable@...r.kernel.org, will@...nel.org
Subject: Re: [PATCH v2] iommu/iova: Reset max32_alloc_size after cleaning
 rcache in the fail path

On 2022-03-01 01:59, yf.wang--- via iommu wrote:
> From: Yunfei Wang <yf.wang@...iatek.com>
> 
> 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@...iatek.com>
> Cc: <stable@...r.kernel.org> # 5.10.*
> ---
> v2: Cc stable@...r.kernel.org
>      1. This patch needs to be merged stable branch, add stable@...r.kernel.org
>         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;
>   	}
>   
> 
> 
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu

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