linux-kernel - Re: [PATCH] iommu/intel-iommu: set as DUMMY_DEVICE_DOMAIN

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Date:   Tue, 4 Feb 2020 14:11:45 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jian-Hong Pan <jian-hong@...lessm.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux@...lessm.com
Subject: Re: [PATCH] iommu/intel-iommu: set as DUMMY_DEVICE_DOMAIN_INFO if no
 IOMMU

Hi,

On 2020/2/3 17:10, Jian-Hong Pan wrote:
> If the device has no IOMMU, it still invokes iommu_need_mapping during
> intel_alloc_coherent. However, iommu_need_mapping can only check the
> device is DUMMY_DEVICE_DOMAIN_INFO or not. This patch marks the device
> is a DUMMY_DEVICE_DOMAIN_INFO if the device has no IOMMU.
> 
> Signed-off-by: Jian-Hong Pan <jian-hong@...lessm.com>
> ---
>   drivers/iommu/intel-iommu.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 35a4a3abedc6..878bc986a015 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -5612,8 +5612,10 @@ static int intel_iommu_add_device(struct device *dev)
>   	int ret;
>   
>   	iommu = device_to_iommu(dev, &bus, &devfn);
> -	if (!iommu)
> +	if (!iommu) {
> +		dev->archdata.iommu = DUMMY_DEVICE_DOMAIN_INFO;

Is this a DMA capable device? I am afraid some real bugs might be
covered up if we marking the device as IOMMU dummy here.

Best regards,
baolu

>   		return -ENODEV;
> +	}
>   
>   	iommu_device_link(&iommu->iommu, dev);
>   
>