Re: [PATCH] iommu/vt-d: Handle hotplug devices' default identity mapping setting

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi,

On 2/22/19 10:44 AM, James Dong wrote:
> With specific Linux command line option such as "iommu=pt", some types
> of hotplug devices will be assigned to the static 1:1 iommu domain by
> default during kernel init.
> 
> If such a hotplug device is rescanned after being removed, for example,
> with following sample commands:
>    echo 1 > /sys/bus/pci/devices/0000\:03\:00.1/remove
>    echo 1 > /sys/bus/pci/rescan
> , an iommu group for this hotplug device will be added without attaching
> it to the default static 1:1 domain. As a result, this device's I/O
> operation won't work.

What does "I/O operation won't work" exactly mean here? Do you see any
IOMMU fault message? Or, something doesn't work as expected?

> 
> Keep hotplug devices with default static 1:1 iommu mapping in their default
> domain after such hotplug devices are rescanned.
> 
> Signed-off-by: James Dong <xmdong@google.com>
> Reported-by: Jis Ben <jisben@google.com>
> ---
>   drivers/iommu/intel-iommu.c | 14 +++++++++++++-
>   1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 78188bf7e90d..4b02949e58ca 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -5230,6 +5230,7 @@ static int intel_iommu_add_device(struct device *dev)
>   	struct intel_iommu *iommu;
>   	struct iommu_group *group;
>   	u8 bus, devfn;
> +	int ret = 0;
>   
>   	iommu = device_to_iommu(dev, &bus, &devfn);
>   	if (!iommu)
> @@ -5242,8 +5243,19 @@ static int intel_iommu_add_device(struct device *dev)
>   	if (IS_ERR(group))
>   		return PTR_ERR(group);
>   
> +	if (!iommu_group_default_domain(group) &&
> +	    !find_domain(dev) && iommu_should_identity_map(dev, 0)) {
> +		ret = domain_add_dev_info(si_domain, dev);
> +		if (!ret)
> +			pr_info("identity mapping for device %s\n",
> +				dev_name(dev));
> +		else
> +			pr_info("identity mapping failed (%d) for device %s\n",
> +				ret, dev_name(dev));
> +	}
> +

I am not sure about whether this is a good place to fix this problem
before Intel IOMMU driver switches to default domain.

Do you mind checking this?

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 6ecdcf8fc8c0..f62f30bc1339 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2632,6 +2632,9 @@ static struct dmar_domain 
*find_or_alloc_domain(struct device *dev, int gaw)
                         goto out;
         }

+       if (!iommu_should_identity_map(dev, 0))
+               return si_domain;
+
         /* Allocate and initialize new domain for the device */
         domain = alloc_domain(0);
         if (!domain)

Best regards,
Lu Baolu