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

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