linux-kernel - Re: [PATCH v2 4/7] iommu: Let iommu.strict override ops->def_domain

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Date:   Thu, 17 Nov 2022 09:55:25 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>, iommu@...ts.linux.dev,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>
Cc:     baolu.lu@...ux.intel.com, Pierre Morel <pmorel@...ux.ibm.com>,
        linux-s390@...r.kernel.org, borntraeger@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, linux-kernel@...r.kernel.org,
        Julian Ruess <julianr@...ux.ibm.com>
Subject: Re: [PATCH v2 4/7] iommu: Let iommu.strict override
 ops->def_domain_type

On 2022/11/17 1:16, Niklas Schnelle wrote:
> When iommu.strict=1 is set or iommu_set_dma_strict() was called we
> should use IOMMU_DOMAIN_DMA irrespective of ops->def_domain_type.
> 
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---
>   drivers/iommu/iommu.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 65a3b3d886dc..d9bf94d198df 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1562,6 +1562,9 @@ static int iommu_get_def_domain_type(struct device *dev)
>   {
>   	const struct iommu_ops *ops = dev_iommu_ops(dev);
>   
> +	if (iommu_dma_strict)
> +		return IOMMU_DOMAIN_DMA;

If any quirky device must work in IOMMU identity mapping mode, this
might introduce functional regression. At least for VT-d platforms, some
devices do require IOMMU identity mapping mode for functionality.

> +
>   	if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted)
>   		return IOMMU_DOMAIN_DMA;
>   

Best regards,
baolu