Re: [PATCH RFC 10/11] iommu: Make IOPF handling framework generic

[Lu Baolu <baolu.lu@linux.intel.com>]

On 2022/3/21 20:50, Jason Gunthorpe wrote:
> On Sun, Mar 20, 2022 at 02:40:29PM +0800, Lu Baolu wrote:
> 
>> +static enum iommu_page_response_code
>> +iommu_sva_handle_iopf(struct iommu_fault *fault, void *data)
>> +{
>> +	vm_fault_t ret;
>> +	struct mm_struct *mm;
>> +	struct vm_area_struct *vma;
>> +	unsigned int access_flags = 0;
>> +	struct iommu_domain *domain = data;
> 
> Why is the iommu_domain not passed in as a fully typed object? I would
> think data should some opaque value used by non-sva cases.

The "data" is set together with the fault handler when the caller
installs a fault handler for an iommu domain. We will add a generic
interface to install fault handler for an iommu domain later when a real
non-sva case comes.

> 
> What is the lifetime model here anyhow?

I simply thought that the device driver should guarantee that there are
no pending faults after sva_unbind(). This is insufficient. I need to
rework this.

> 
>> +	unsigned int fault_flags = FAULT_FLAG_REMOTE;
>> +	struct iommu_fault_page_request *prm = &fault->prm;
>> +	enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
>> +
>> +	if (!(prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID))
>> +		return status;
>> +
>> +	mm = domain->sva_cookie;
>> +	if (IS_ERR_OR_NULL(mm))
> 
> Do not use this function
> 
> Do not store err pointers in structs.

Sure.

> 
>> +out_put_mm:
>> +	mmap_read_unlock(mm);
>> +	mmput(mm);
> 
> mm structs are weird, they have two refcounts.
> 
> The 'sva_cookie' should hold a mmgrab/mmdrop() refcount to keep the
> pointer alive but to touch the mmap lock you have to upgrade it to a
> refcount that prevents destruction using mmget_not_zero() just for
> this short period.

Yes. Will look into it.

Best regards,
baolu