linux-kernel - Re: [PATCH v3 1/7] iommu/vt-d: Require DMA domain if hardware not support passthrough

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Message-ID: <6t4vbpxwibd2egshbgro3mixmnfdhioy57fb46bpc35hjhzdoi@l2ck53gfq63z>
Date: Wed, 14 Aug 2024 09:13:10 -0700
From: Jerry Snitselaar <jsnitsel@...hat.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	Robin Murphy <robin.murphy@....com>, Jason Gunthorpe <jgg@...pe.ca>, 
	Kevin Tian <kevin.tian@...el.com>, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/7] iommu/vt-d: Require DMA domain if hardware not
 support passthrough

On Tue, Aug 06, 2024 at 10:39:35AM GMT, Lu Baolu wrote:
> The iommu core defines the def_domain_type callback to query the iommu
> driver about hardware capability and quirks. The iommu driver should
> declare IOMMU_DOMAIN_DMA requirement for hardware lacking pass-through
> capability.
> 
> Earlier VT-d hardware implementations did not support pass-through
> translation mode. The iommu driver relied on a paging domain with all
> physical system memory addresses identically mapped to the same IOVA
> to simulate pass-through translation before the def_domain_type was
> introduced and it has been kept until now. It's time to adjust it now
> to make the Intel iommu driver follow the def_domain_type semantics.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>

Reviewed-by: Jerry Snitselaar <jsnitsel@...hat.com>

> ---
>  drivers/iommu/intel/iommu.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 9ff8b83c19a3..90ad794a1be7 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2149,6 +2149,16 @@ static bool device_rmrr_is_relaxable(struct device *dev)
>  
>  static int device_def_domain_type(struct device *dev)
>  {
> +	struct device_domain_info *info = dev_iommu_priv_get(dev);
> +	struct intel_iommu *iommu = info->iommu;
> +
> +	/*
> +	 * Hardware does not support the passthrough translation mode.
> +	 * Always use a dynamaic mapping domain.
> +	 */
> +	if (!ecap_pass_through(iommu->ecap))
> +		return IOMMU_DOMAIN_DMA;
> +
>  	if (dev_is_pci(dev)) {
>  		struct pci_dev *pdev = to_pci_dev(dev);
>  
> -- 
> 2.34.1
>