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

[Baolu Lu]

On 2022/7/23 22:33, Jason Gunthorpe wrote:
> 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?

The iommu_fault_handler_t is for report_iommu_fault() which could be
replaced with the newer iommu_report_device_fault().

https://lore.kernel.org/linux-iommu/Yo4Nw9QyllT1RZbd@myrica/

> > +/*
> > + * 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.

Yes. Updated.

Best regards,
baolu