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

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Date: Sun, 10 Mar 2024 21:05:58 +0800
From: Yi Liu <yi.l.liu@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <joro@...tes.org>, <alex.williamson@...hat.com>, <kevin.tian@...el.com>,
	<robin.murphy@....com>, <baolu.lu@...ux.intel.com>, <cohuck@...hat.com>,
	<eric.auger@...hat.com>, <nicolinc@...dia.com>, <kvm@...r.kernel.org>,
	<mjrosato@...ux.ibm.com>, <chao.p.peng@...ux.intel.com>,
	<yi.y.sun@...ux.intel.com>, <peterx@...hat.com>, <jasowang@...hat.com>,
	<shameerali.kolothum.thodi@...wei.com>, <lulu@...hat.com>,
	<suravee.suthikulpanit@....com>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
	<zhenzhong.duan@...el.com>, <joao.m.martins@...cle.com>,
	<xin.zeng@...el.com>, <yan.y.zhao@...el.com>
Subject: Re: [PATCH 1/8] iommu: Introduce a replace API for device pasid

On 2024/1/16 01:19, Jason Gunthorpe wrote:
> On Sun, Nov 26, 2023 at 10:34:21PM -0800, Yi Liu wrote:
>> +int iommu_replace_device_pasid(struct iommu_domain *domain,
>> +			       struct device *dev, ioasid_t pasid)
>> +{
>> +	struct iommu_group *group = dev->iommu_group;
>> +	struct iommu_domain *old_domain;
>> +	int ret;
>> +
>> +	if (!domain)
>> +		return -EINVAL;
>> +
>> +	if (!group)
>> +		return -ENODEV;
>> +
>> +	mutex_lock(&group->mutex);
>> +	__iommu_remove_group_pasid(group, pasid);
> 
> It is not replace if you do remove first.
> 
> Replace must just call set_dev_pasid and nothing much else..

Seems uneasy to do it so far. The VT-d driver needs to get the old domain
first in order to do replacement. However, VT-d driver does not track the
attached domains of pasids. It gets domain of a pasid
by iommu_get_domain_for_dev_pasid(). Like intel_iommu_remove_dev_pasid)
in link [1]. While the iommu layer exchanges the domain in the
group->pasid_array before calling into VT-d driver. So when calling into
VT-d driver, the domain got by iommu_get_domain_for_dev_pasid() is already
the new domain. To solve it, we may need to let VT-d driver have its
own tracking on the domains. How about your thoughts? @Jason, @Kevin, @Baoplu?

[1] 
https://github.com/torvalds/linux/blob/master/drivers/iommu/intel/iommu.c#L4621C19-L4621C20

-- 
Regards,
Yi Liu