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SubjectRe: [PATCH v4 20/22] iommu/vt-d: Add bind guest PASID support
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Hi Jacob,

On 6/28/19 4:22 AM, Jacob Pan wrote:
>>> + }
>>> + refcount_set(&svm->refs, 0);
>>> + ioasid_set_data(data->hpasid, svm);
>>> + INIT_LIST_HEAD_RCU(&svm->devs);
>>> + INIT_LIST_HEAD(&svm->list);
>>> +
>>> + mmput(svm->mm);
>>> + }
>>> + sdev = kzalloc(sizeof(*sdev), GFP_KERNEL);
>>> + if (!sdev) {
>>> + ret = -ENOMEM;
>>> + goto out;
>> I think you need to clean up svm if its device list is empty here, as
>> you said above:
>>
> No, we come here only if the device list is not empty and the new
> device to bind is different than any existing device in the list. If we
> cannot allocate memory for the new device, should not free the existing
> SVM, right?
>

I'm sorry, but the code doesn't show this. We come here even an svm data
structure was newly created with an empty device list. I post the code
below to ensure that we are reading a same piece of code.

mutex_lock(&pasid_mutex);
svm = ioasid_find(NULL, data->hpasid, NULL);
if (IS_ERR(svm)) {
ret = PTR_ERR(svm);
goto out;
}
if (svm) {
/*
* If we found svm for the PASID, there must be at
* least one device bond, otherwise svm should be freed.
*/
BUG_ON(list_empty(&svm->devs));

for_each_svm_dev() {
/* In case of multiple sub-devices of the same
pdev assigned, we should
* allow multiple bind calls with the same
PASID and pdev.
*/
sdev->users++;
goto out;
}
} else {
/* We come here when PASID has never been bond to a
device. */
svm = kzalloc(sizeof(*svm), GFP_KERNEL);
if (!svm) {
ret = -ENOMEM;
goto out;
}
/* REVISIT: upper layer/VFIO can track host process
that bind the PASID.
* ioasid_set = mm might be sufficient for vfio to
check pasid VMM
* ownership.
*/
svm->mm = get_task_mm(current);
svm->pasid = data->hpasid;
if (data->flags & IOMMU_SVA_GPASID_VAL) {
svm->gpasid = data->gpasid;
svm->flags &= SVM_FLAG_GUEST_PASID;
}
refcount_set(&svm->refs, 0);
ioasid_set_data(data->hpasid, svm);
INIT_LIST_HEAD_RCU(&svm->devs);
INIT_LIST_HEAD(&svm->list);

mmput(svm->mm);
}
sdev = kzalloc(sizeof(*sdev), GFP_KERNEL);
if (!sdev) {
ret = -ENOMEM;
goto out;
}
sdev->dev = dev;
sdev->users = 1;

Best regards,
Baolu

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