Re: [PATCH v7 08/10] iommu: Prepare IOMMU domain for IOPF

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

On Thu, May 19, 2022 at 03:20:45PM +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.
> 
> Suggested-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  include/linux/iommu.h         |  3 ++
>  drivers/iommu/io-pgfault.c    |  7 ++++
>  drivers/iommu/iommu-sva-lib.c | 65 +++++++++++++++++++++++++++++++++++
>  3 files changed, 75 insertions(+)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index e4ce2fe0e144..45f274b2640d 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -100,6 +100,9 @@ struct iommu_domain {
>  	void *handler_token;
>  	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;
>  };
>  
>  static inline bool iommu_is_dma_domain(struct iommu_domain *domain)
> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
> index 1df8c1dcae77..aee9e033012f 100644
> --- a/drivers/iommu/io-pgfault.c
> +++ b/drivers/iommu/io-pgfault.c
> @@ -181,6 +181,13 @@ static void iopf_handle_group(struct work_struct *work)
>   * request completes, outstanding faults will have been dealt with by the time
>   * the PASID is freed.
>   *
> + * Any valid page fault will be eventually routed to an iommu domain and the
> + * page fault handler installed there will get called. The users of this
> + * handling framework should guarantee that the iommu domain could only be
> + * freed after the device has stopped generating page faults (or the iommu
> + * hardware has been set to block the page faults) and the pending page faults
> + * have been flushed.
> + *
>   * Return: 0 on success and <0 on error.
>   */
>  int iommu_queue_iopf(struct iommu_fault *fault, void *cookie)
> diff --git a/drivers/iommu/iommu-sva-lib.c b/drivers/iommu/iommu-sva-lib.c
> index 568e0f64edac..317ab8e8c149 100644
> --- a/drivers/iommu/iommu-sva-lib.c
> +++ b/drivers/iommu/iommu-sva-lib.c
> @@ -72,6 +72,69 @@ struct mm_struct *iommu_sva_find(ioasid_t pasid)
>  }
>  EXPORT_SYMBOL_GPL(iommu_sva_find);
>  
> +/*
> + * I/O page fault handler for SVA
> + *
> + * Copied from io-pgfault.c with mmget_not_zero() added before
> + * mmap_read_lock().

Comment doesn't really belong here, maybe better in the commit message.
Apart from that

Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

> + */
> +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;
> +	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_to_mm(domain);
> +	if (IS_ERR_OR_NULL(mm) || !mmget_not_zero(mm))
> +		return status;
> +
> +	mmap_read_lock(mm);
> +
> +	vma = find_extend_vma(mm, prm->addr);
> +	if (!vma)
> +		/* Unmapped area */
> +		goto out_put_mm;
> +
> +	if (prm->perm & IOMMU_FAULT_PERM_READ)
> +		access_flags |= VM_READ;
> +
> +	if (prm->perm & IOMMU_FAULT_PERM_WRITE) {
> +		access_flags |= VM_WRITE;
> +		fault_flags |= FAULT_FLAG_WRITE;
> +	}
> +
> +	if (prm->perm & IOMMU_FAULT_PERM_EXEC) {
> +		access_flags |= VM_EXEC;
> +		fault_flags |= FAULT_FLAG_INSTRUCTION;
> +	}
> +
> +	if (!(prm->perm & IOMMU_FAULT_PERM_PRIV))
> +		fault_flags |= FAULT_FLAG_USER;
> +
> +	if (access_flags & ~vma->vm_flags)
> +		/* Access fault */
> +		goto out_put_mm;
> +
> +	ret = handle_mm_fault(vma, prm->addr, fault_flags, NULL);
> +	status = ret & VM_FAULT_ERROR ? IOMMU_PAGE_RESP_INVALID :
> +		IOMMU_PAGE_RESP_SUCCESS;
> +
> +out_put_mm:
> +	mmap_read_unlock(mm);
> +	mmput(mm);
> +
> +	return status;
> +}
> +
>  /*
>   * IOMMU SVA driver-oriented interfaces
>   */
> @@ -94,6 +157,8 @@ iommu_sva_alloc_domain(struct bus_type *bus, struct mm_struct *mm)
>  	domain = &sva_domain->domain;
>  	domain->type = IOMMU_DOMAIN_SVA;
>  	domain->ops = bus->iommu_ops->sva_domain_ops;
> +	domain->iopf_handler = iommu_sva_handle_iopf;
> +	domain->fault_data = domain;
>  
>  	return domain;
>  }
> -- 
> 2.25.1
> 
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