linux-kernel - Re: [PATCH v3 2/4] dma-iommu: Add iommu_dma_opt_mapping

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Message-ID: <d7a72f92-15c9-1d58-c711-83c47444094e@acm.org>
Date:   Wed, 8 Jun 2022 10:26:40 -0700
From:   Bart Van Assche <bvanassche@....org>
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, robin.murphy@....com
Cc:     linux-scsi@...r.kernel.org, linux-doc@...r.kernel.org,
        liyihang6@...ilicon.com, linux-kernel@...r.kernel.org,
        linux-ide@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: Re: [PATCH v3 2/4] dma-iommu: Add iommu_dma_opt_mapping_size()

On 6/6/22 02:30, John Garry via iommu wrote:
> +unsigned long iova_rcache_range(void)
> +{
> +	return PAGE_SIZE << (IOVA_RANGE_CACHE_MAX_SIZE - 1);
> +}

My understanding is that iova cache entries may be smaller than 
IOVA_RANGE_CACHE_MAX_SIZE and hence that even if code that uses the DMA 
mapping API respects this limit that a cache miss can still happen.

Thanks,

Bart.