Re: [PATCH v10 10/12] iommu: Prepare IOMMU domain for IOPF

[Jason Gunthorpe]

On Tue, Jul 05, 2022 at 01:07:08PM +0800, Lu Baolu wrote:
> This adds some mechanisms around the iommu_domain so that the I/O page
> fault handling framework could route a page fault to the domain and
> call the fault handler from it.
> 
> Add pointers to the page fault handler and its private data in struct
> iommu_domain. The fault handler will be called with the private data
> as a parameter once a page fault is routed to the domain. Any kernel
> component which owns an iommu domain could install handler and its
> private parameter so that the page fault could be further routed and
> handled.
> 
> This also prepares the SVA implementation to be the first consumer of
> the per-domain page fault handling model. The I/O page fault handler
> for SVA is copied to the SVA file with mmget_not_zero() added before
> mmap_read_lock().
> 
> Suggested-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Reviewed-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> Tested-by: Zhangfei Gao <zhangfei.gao@xxxxxxxxxx>
> Tested-by: Tony Zhu <tony.zhu@xxxxxxxxx>
> ---
>  include/linux/iommu.h         |  3 ++
>  drivers/iommu/iommu-sva-lib.h |  8 +++++
>  drivers/iommu/io-pgfault.c    |  7 +++++
>  drivers/iommu/iommu-sva-lib.c | 58 +++++++++++++++++++++++++++++++++++
>  drivers/iommu/iommu.c         |  4 +++
>  5 files changed, 80 insertions(+)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index ae0cfca064e6..47610f21d451 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -105,6 +105,9 @@ struct iommu_domain {
>  	unsigned long pgsize_bitmap;	/* Bitmap of page sizes in use */
>  	struct iommu_domain_geometry geometry;
>  	struct iommu_dma_cookie *iova_cookie;
> +	enum iommu_page_response_code (*iopf_handler)(struct iommu_fault *fault,
> +						      void *data);
> +	void *fault_data;
>  	union {
>  		struct {
>  			iommu_fault_handler_t handler;

Why do we need two falut callbacks? The only difference is that one is
recoverable and the other is not, right?

Can we run both down the same op?

> +/*
> + * I/O page fault handler for SVA
> + */
> +enum iommu_page_response_code
> +iommu_sva_handle_iopf(struct iommu_fault *fault, void *data)
> +{
> +	vm_fault_t ret;
> +	struct vm_area_struct *vma;
> +	struct mm_struct *mm = data;
> +	unsigned int access_flags = 0;
> +	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;
> +
> +	if (IS_ERR_OR_NULL(mm) || !mmget_not_zero(mm))

Do not use IS_ERR_ON_NULL. mm should never be null here since the
fault handler should have been removed from the domain before the
fault_data is changed.

Jason