linux-kernel - Re: [PATCH 1/8] iommu: Introduce a replace API for device pasid

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Date: Tue, 19 Mar 2024 15:29:39 +0800
From: Yi Liu <yi.l.liu@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Baolu Lu <baolu.lu@...ux.intel.com>, "Tian, Kevin" <kevin.tian@...el.com>,
	"joro@...tes.org" <joro@...tes.org>, "alex.williamson@...hat.com"
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 Zhenzhong" <zhenzhong.duan@...el.com>, "joao.m.martins@...cle.com"
	<joao.m.martins@...cle.com>, "Zeng, Xin" <xin.zeng@...el.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>
Subject: Re: [PATCH 1/8] iommu: Introduce a replace API for device pasid

On 2024/3/19 00:52, Jason Gunthorpe wrote:
> On Wed, Mar 13, 2024 at 04:11:41PM +0800, Yi Liu wrote:
> 
>> yes. how about your opinion? @Jason. I noticed the set_dev_pasid callback
>> and pasid_array update is under the group->lock, so update it should be
>> fine to adjust the order to update pasid_array after set_dev_pasid returns.
> 
> Yes, it makes some sense
> 
> But, also I would like it very much if we just have the core pass in
> the actual old domain as a an addition function argument.

ok, this works too. For normal attach, just pass in a NULL old domain.

> I think we have some small mistakes in multi-device group error
> unwinding for remove because the global xarray can't isn't actually
> going to be correct in all scenarios.

do you mean the __iommu_remove_group_pasid() call in the below function?
Currently, it is called when __iommu_set_group_pasid() failed. However,
__iommu_set_group_pasid() may need to do remove itself when error happens,
so the helper can be more self-contained. Or you mean something else?

int iommu_attach_device_pasid(struct iommu_domain *domain,
			      struct device *dev, ioasid_t pasid)
{
	/* Caller must be a probed driver on dev */
	struct iommu_group *group = dev->iommu_group;
	void *curr;
	int ret;

	if (!domain->ops->set_dev_pasid)
		return -EOPNOTSUPP;

	if (!group)
		return -ENODEV;

	if (!dev_has_iommu(dev) || dev_iommu_ops(dev) != domain->owner)
		return -EINVAL;

	mutex_lock(&group->mutex);
	curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain, GFP_KERNEL);
	if (curr) {
		ret = xa_err(curr) ? : -EBUSY;
		goto out_unlock;
	}

	ret = __iommu_set_group_pasid(domain, group, pasid);
	if (ret) {
		__iommu_remove_group_pasid(group, pasid);
		xa_erase(&group->pasid_array, pasid);
	}
out_unlock:
	mutex_unlock(&group->mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(iommu_attach_device_pasid);

https://github.com/torvalds/linux/blob/b3603fcb79b1036acae10602bffc4855a4b9af80/drivers/iommu/iommu.c#L3376

-- 
Regards,
Yi Liu