linux-kernel - Re: [PATCH v5 02/10] iommu/vt-d: Use per-device dma

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Message-ID: <20190725054413.GC24527@lst.de>
Date:   Thu, 25 Jul 2019 07:44:13 +0200
From:   Christoph Hellwig <hch@....de>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Christoph Hellwig <hch@....de>, ashok.raj@...el.com,
        jacob.jun.pan@...el.com, alan.cox@...el.com, kevin.tian@...el.com,
        mika.westerberg@...ux.intel.com, Ingo Molnar <mingo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        pengfei.xu@...el.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Jonathan Corbet <corbet@....net>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH v5 02/10] iommu/vt-d: Use per-device dma_ops

>  /* Check if the dev needs to go through non-identity map and unmap process.*/
>  static bool iommu_need_mapping(struct device *dev)
>  {
> -	int ret;
> -
>  	if (iommu_dummy(dev))
>  		return false;
>  
> -	ret = identity_mapping(dev);
> -	if (ret) {
> -		u64 dma_mask = *dev->dma_mask;
> -
> -		if (dev->coherent_dma_mask && dev->coherent_dma_mask < dma_mask)
> -			dma_mask = dev->coherent_dma_mask;
> -
> -		if (dma_mask >= dma_get_required_mask(dev))
> -			return false;

Don't we need to keep this bit so that we still allow the IOMMU
to act if the device has a too small DMA mask to address all memory in
the system, even if if it should otherwise be identity mapped?