linux-kernel - Re: [PATCH] iommu: Sanity check on param list for iommu_get_resv

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Date:   Thu, 28 Sep 2023 17:25:02 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Dawei Li <set_pte_at@...look.com>
Cc:     baolu.lu@...ux.intel.com, joro@...tes.org, will@...nel.org,
        robin.murphy@....com, jgg@...dia.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu: Sanity check on param list for
 iommu_get_resv_regions

On 2023/9/28 16:57, Dawei Li wrote:
> On Thu, Sep 28, 2023 at 09:33:29AM +0800, Baolu Lu wrote:
>> On 9/27/23 10:25 PM, Dawei Li wrote:
>>> In iommu_get_resv_regions(), param list is an argument supplied by caller,
>>> into which callee is supposed to insert resv regions.
>>>
>>> In other words, this 'list' argument is expected to be an empty list,
>>> so make an explicit annotation on it.
>>>
>>> Signed-off-by: Dawei Li<set_pte_at@...look.com>
>>> ---
>>>    drivers/iommu/iommu.c | 9 +++++----
>>>    1 file changed, 5 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>> index 1ecac2b5c54f..a01c4a7a9d19 100644
>>> --- a/drivers/iommu/iommu.c
>>> +++ b/drivers/iommu/iommu.c
>>> @@ -813,7 +813,7 @@ int iommu_get_group_resv_regions(struct iommu_group *group,
>>>    	mutex_lock(&group->mutex);
>>>    	for_each_group_device(group, device) {
>>> -		struct list_head dev_resv_regions;
>>> +		LIST_HEAD(dev_resv_regions);
>>>    		/*
>>>    		 * Non-API groups still expose reserved_regions in sysfs,
>>> @@ -822,7 +822,6 @@ int iommu_get_group_resv_regions(struct iommu_group *group,
>>>    		if (!device->dev->iommu)
>>>    			break;
>>> -		INIT_LIST_HEAD(&dev_resv_regions);
>>>    		iommu_get_resv_regions(device->dev, &dev_resv_regions);
>>>    		ret = iommu_insert_device_resv_regions(&dev_resv_regions, head);
>>>    		iommu_put_resv_regions(device->dev, &dev_resv_regions);
>>> @@ -1061,12 +1060,11 @@ static int iommu_create_device_direct_mappings(struct iommu_domain *domain,
>>>    					       struct device *dev)
>>>    {
>>>    	struct iommu_resv_region *entry;
>>> -	struct list_head mappings;
>>>    	unsigned long pg_size;
>>> +	LIST_HEAD(mappings);
>>>    	int ret = 0;
>>>    	pg_size = domain->pgsize_bitmap ? 1UL << __ffs(domain->pgsize_bitmap) : 0;
>>> -	INIT_LIST_HEAD(&mappings);
>>>    	if (WARN_ON_ONCE(iommu_is_dma_domain(domain) && !pg_size))
>>>    		return -EINVAL;
>>> @@ -2813,6 +2811,9 @@ void iommu_get_resv_regions(struct device *dev, struct list_head *list)
>>>    {
>>>    	const struct iommu_ops *ops = dev_iommu_ops(dev);
>>> +	if (WARN_ON(!list_empty(list)))
>>> +		return;
>> I don't understand why the input list*must*  be empty. This interface
> Because @list is an output-only argument, which is supposed to be filled
> by caller(inserting elements into it). If it's not empty, it's an inputing
> argument, in which case caller will take existing node (in @list) into account,
> and insert new nodes before/after them.
> Please lemme put it another way, if list argment is not empty:
> 
> Before calling:
> list: head->A
> 
> After calling
> list: head->A->B->C
> 
> It will confuse caller cuz it can't tell whether A is a valid returned
> by callee.

I see. Thank you for the explanation.

Best regards,
baolu