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

[Jason Gunthorpe]

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.

What is the lifetime model here anyhow?

> +	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.

> +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.

Jason