Re: [RFC PATCH 2/4] PCI: Add "pci=iommu_passthrough=" parameter for iommu passthrough

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Jan 01, 2020 at 01:26:46PM +0800, Lu Baolu wrote:
> The new parameter takes a list of devices separated by a semicolon.
> Each device specified will have its iommu_passthrough bit in struct
> device set. This is very similar to the existing 'disable_acs_redir'
> parameter.
> 
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |  5 +++
>  drivers/pci/pci.c                             | 34 +++++++++++++++++++
>  drivers/pci/pci.h                             |  1 +
>  drivers/pci/probe.c                           |  2 ++
>  4 files changed, 42 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index ade4e6ec23e0..d3edc2cb6696 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3583,6 +3583,11 @@
>  				may put more devices in an IOMMU group.
>  		force_floating	[S390] Force usage of floating interrupts.
>  		nomio		[S390] Do not use MIO instructions.
> +		iommu_passthrough=<pci_dev>[; ...]
> +				Specify one or more PCI devices (in the format
> +				specified above) separated by semicolons.
> +				Each device specified will bypass IOMMU DMA
> +				translation.
>  
>  	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power
>  			Management.
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 90dbd7c70371..05bf3f4acc36 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -6401,6 +6401,37 @@ void __weak pci_fixup_cardbus(struct pci_bus *bus)
>  }
>  EXPORT_SYMBOL(pci_fixup_cardbus);
>  
> +static const char *iommu_passthrough_param;
> +bool pci_iommu_passthrough_match(struct pci_dev *dev)
> +{
> +	int ret = 0;
> +	const char *p = iommu_passthrough_param;
> +
> +	if (!p)
> +		return false;
> +
> +	while (*p) {
> +		ret = pci_dev_str_match(dev, p, &p);
> +		if (ret < 0) {
> +			pr_info_once("PCI: Can't parse iommu_passthrough parameter: %s\n",
> +				     iommu_passthrough_param);
> +
> +			break;
> +		} else if (ret == 1) {
> +			pci_info(dev, "PCI: IOMMU passthrough\n");
> +			return true;
> +		}
> +
> +		if (*p != ';' && *p != ',') {
> +			/* End of param or invalid format */
> +			break;
> +		}
> +		p++;
> +	}
> +
> +	return false;
> +}

This duplicates a lot of the code in pci_disable_acs_redir().  That
needs to be factored out somehow so we don't duplicate it.

Bjorn