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

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Date:   Sat, 18 Jan 2020 10:04:55 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        ashok.raj@...el.com, jacob.jun.pan@...el.com, kevin.tian@...el.com,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/4] PCI: Add "pci=iommu_passthrough=" parameter for
 iommu passthrough

Hi Bjorn,

On 1/18/20 8:18 AM, Bjorn Helgaas wrote:
> 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@...ux.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.
> 

Sure. I will try to refactor the code in the next version.

> Bjorn
> 

Best regards,
baolu