Re: [PATCH v8 02/11] iommu: Add max_pasids field in struct dev_iommu

Baolu Lu
2022-06-10T06:47:08Z

On 2022/6/10 03:01, Raj, Ashok wrote:
> On Tue, Jun 07, 2022 at 09:49:33AM +0800, Lu Baolu wrote:
>> Use this field to save the number of PASIDs that a device is able to
>> consume. It is a generic attribute of a device and lifting it into the
>> per-device dev_iommu struct could help to avoid the boilerplate code
>> in various IOMMU drivers.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>> include/linux/iommu.h | 2 ++
>> drivers/iommu/iommu.c | 26 ++++++++++++++++++++++++++
>> 2 files changed, 28 insertions(+)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 03fbb1b71536..d50afb2c9a09 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -364,6 +364,7 @@ struct iommu_fault_param {
>> * @fwspec: IOMMU fwspec data
>> * @iommu_dev: IOMMU device this device is linked to
>> * @priv: IOMMU Driver private data
>> + * @max_pasids: number of PASIDs device can consume
>> *
>> * TODO: migrate other per device data pointers under iommu_dev_data, e.g.
>> * struct iommu_group *iommu_group;
>> @@ -375,6 +376,7 @@ struct dev_iommu {
>> struct iommu_fwspec *fwspec;
>> struct iommu_device *iommu_dev;
>> void *priv;
>> + u32 max_pasids;
>> };
>>
>> int iommu_device_register(struct iommu_device *iommu,
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 847ad47a2dfd..adac85ccde73 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -20,6 +20,7 @@
>> #include <linux/idr.h>
>> #include <linux/err.h>
>> #include <linux/pci.h>
>> +#include <linux/pci-ats.h>
>
> Is this needed for this patch?

Yes. It's for pci_max_pasids().

>
>> #include <linux/bitops.h>
>> #include <linux/property.h>
>> #include <linux/fsl/mc.h>
>> @@ -218,6 +219,30 @@ static void dev_iommu_free(struct device *dev)
>> kfree(param);
>> }
>>
>> +static u32 dev_iommu_get_max_pasids(struct device *dev)
>> +{
>> + u32 max_pasids = dev->iommu->iommu_dev->max_pasids;
>> + u32 num_bits;
>> + int ret;
>> +
>> + if (!max_pasids)
>> + return 0;
>> +
>> + if (dev_is_pci(dev)) {
>> + ret = pci_max_pasids(to_pci_dev(dev));
>> + if (ret < 0)
>> + return 0;
>> +
>> + return min_t(u32, max_pasids, ret);
>
> Ah.. that answers my other question to consider device pasid-max. I guess
> if we need any enforcement of restricting devices that aren't supporting
> the full PASID, that will be done by some higher layer?

The mm->pasid style of SVA is explicitly enabled through
iommu_dev_enable_feature(IOMMU_DEV_FEAT_SVA). The IOMMU driver specific
restriction might be put there?

>
> too many returns in this function, maybe setup all returns to the end of
> the function might be elegant?

I didn't find cleanup room after a quick scan of the code. But sure, let
me go through code again offline.

>
>> + }
>> +
>> + ret = device_property_read_u32(dev, "pasid-num-bits", &num_bits);
>> + if (ret)
>> + return 0;
>> +
>> + return min_t(u32, max_pasids, 1UL << num_bits);
>> +}
>> +
>> static int __iommu_probe_device(struct device *dev, struct list_head *group_list)
>> {
>> const struct iommu_ops *ops = dev->bus->iommu_ops;
>> @@ -243,6 +268,7 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list
>> }
>>
>> dev->iommu->iommu_dev = iommu_dev;
>> + dev->iommu->max_pasids = dev_iommu_get_max_pasids(dev);
>>
>> group = iommu_group_get_for_dev(dev);
>> if (IS_ERR(group)) {
>> --
>> 2.25.1
>>

Best regards,
Baolu