linux-kernel - Re: [PATCH v7 3/3] iommu/tegra-smmu: Add PCI support

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Date:   Thu, 15 Oct 2020 10:55:52 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     thierry.reding@...il.com, joro@...tes.org, digetx@...il.com,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, jonathanh@...dia.com
Subject: Re: [PATCH v7 3/3] iommu/tegra-smmu: Add PCI support

On 2020-10-15 05:13, Nicolin Chen wrote:
> On Wed, Oct 14, 2020 at 06:42:36PM +0100, Robin Murphy wrote:
>> On 2020-10-09 17:19, Nicolin Chen wrote:
>>> This patch simply adds support for PCI devices.
>>>
>>> Reviewed-by: Dmitry Osipenko <digetx@...il.com>
>>> Tested-by: Dmitry Osipenko <digetx@...il.com>
>>> Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
>>> ---
>>>
>>> Changelog
>>> v6->v7
>>>    * Renamed goto labels, suggested by Thierry.
>>> v5->v6
>>>    * Added Dmitry's Reviewed-by and Tested-by.
>>> v4->v5
>>>    * Added Dmitry's Reviewed-by
>>> v3->v4
>>>    * Dropped !iommu_present() check
>>>    * Added CONFIG_PCI check in the exit path
>>> v2->v3
>>>    * Replaced ternary conditional operator with if-else in .device_group()
>>>    * Dropped change in tegra_smmu_remove()
>>> v1->v2
>>>    * Added error-out labels in tegra_smmu_probe()
>>>    * Dropped pci_request_acs() since IOMMU core would call it.
>>>
>>>    drivers/iommu/tegra-smmu.c | 35 +++++++++++++++++++++++++----------
>>>    1 file changed, 25 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
>>> index be29f5977145..2941d6459076 100644
>>> --- a/drivers/iommu/tegra-smmu.c
>>> +++ b/drivers/iommu/tegra-smmu.c
>>> @@ -10,6 +10,7 @@
>>>    #include <linux/kernel.h>
>>>    #include <linux/of.h>
>>>    #include <linux/of_device.h>
>>> +#include <linux/pci.h>
>>>    #include <linux/platform_device.h>
>>>    #include <linux/slab.h>
>>>    #include <linux/spinlock.h>
>>> @@ -865,7 +866,11 @@ static struct iommu_group *tegra_smmu_device_group(struct device *dev)
>>>    	group->smmu = smmu;
>>>    	group->soc = soc;
>>> -	group->group = iommu_group_alloc();
>>> +	if (dev_is_pci(dev))
>>> +		group->group = pci_device_group(dev);
>>
>> Just to check, is it OK to have two or more swgroups "owning" the same
>> iommu_group if an existing one gets returned here? It looks like that might
>> not play nice with the use of iommu_group_set_iommudata().
> 
> Do you mean by "gets returned here" the "IS_ERR" check below?

I mean that unlike iommu_group_alloc()/generic_device_group(), 
pci_device_group() may give you back a group that already contains 
another device and has already been set up from that device's 
perspective. This can happen for topological reasons like requester ID 
aliasing through a PCI-PCIe bridge or lack of isolation between functions.

Robin.

>>> +	else
>>> +		group->group = generic_device_group(dev);
>>> +
>>>    	if (IS_ERR(group->group)) {
>>>    		devm_kfree(smmu->dev, group);
>>>    		mutex_unlock(&smmu->lock);