Re: [PATCH v6 05/25] iommu/iopf: Handle mm faults

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

On 2020/4/30 22:34, Jean-Philippe Brucker wrote:
> When a recoverable page fault is handled by the fault workqueue, find the
> associated mm and call handle_mm_fault.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
> v5->v6: select CONFIG_IOMMU_SVA
> ---
>   drivers/iommu/Kconfig      |  1 +
>   drivers/iommu/io-pgfault.c | 79 +++++++++++++++++++++++++++++++++++++-
>   2 files changed, 78 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 4f33e489f0726..1e64ee6592e16 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -109,6 +109,7 @@ config IOMMU_SVA
>   
>   config IOMMU_PAGE_FAULT
>   	bool
> +	select IOMMU_SVA

It would be better to move this to the previous patch.

>   
>   config FSL_PAMU
>   	bool "Freescale IOMMU support"
> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
> index 38732e97faac1..09a71dc4de20a 100644
> --- a/drivers/iommu/io-pgfault.c
> +++ b/drivers/iommu/io-pgfault.c
> @@ -7,9 +7,12 @@
>   
>   #include <linux/iommu.h>
>   #include <linux/list.h>
> +#include <linux/sched/mm.h>
>   #include <linux/slab.h>
>   #include <linux/workqueue.h>
>   
> +#include "iommu-sva.h"
> +
>   /**
>    * struct iopf_queue - IO Page Fault queue
>    * @wq: the fault workqueue
> @@ -68,8 +71,57 @@ static int iopf_complete_group(struct device *dev, struct iopf_fault *iopf,
>   static enum iommu_page_response_code
>   iopf_handle_single(struct iopf_fault *iopf)
>   {
> -	/* TODO */
> -	return -ENODEV;
> +	vm_fault_t ret;
> +	struct mm_struct *mm;
> +	struct vm_area_struct *vma;
> +	unsigned int access_flags = 0;
> +	unsigned int fault_flags = FAULT_FLAG_REMOTE;
> +	struct iommu_fault_page_request *prm = &iopf->fault.prm;
> +	enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
> +
> +	if (!(prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID))
> +		return status;
> +
> +	mm = iommu_sva_find(prm->pasid);
> +	if (IS_ERR_OR_NULL(mm))
> +		return status;
> +
> +	down_read(&mm->mmap_sem);
> +
> +	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);
> +	status = ret & VM_FAULT_ERROR ? IOMMU_PAGE_RESP_INVALID :
> +		IOMMU_PAGE_RESP_SUCCESS;
> +
> +out_put_mm:
> +	up_read(&mm->mmap_sem);
> +	mmput(mm);
> +
> +	return status;
>   }
>   
>   static void iopf_handle_group(struct work_struct *work)
> @@ -104,6 +156,29 @@ static void iopf_handle_group(struct work_struct *work)
>    *
>    * Add a fault to the device workqueue, to be handled by mm.
>    *
> + * This module doesn't handle PCI PASID Stop Marker; IOMMU drivers must discard
> + * them before reporting faults. A PASID Stop Marker (LRW = 0b100) doesn't
> + * expect a response. It may be generated when disabling a PASID (issuing a
> + * PASID stop request) by some PCI devices.
> + *
> + * The PASID stop request is issued by the device driver before unbind(). Once
> + * it completes, no page request is generated for this PASID anymore and
> + * outstanding ones have been pushed to the IOMMU (as per PCIe 4.0r1.0 - 6.20.1
> + * and 10.4.1.2 - Managing PASID TLP Prefix Usage). Some PCI devices will wait
> + * for all outstanding page requests to come back with a response before
> + * completing the PASID stop request. Others do not wait for page responses, and
> + * instead issue this Stop Marker that tells us when the PASID can be
> + * reallocated.
> + *
> + * It is safe to discard the Stop Marker because it is an optimization.
> + * a. Page requests, which are posted requests, have been flushed to the IOMMU
> + *    when the stop request completes.
> + * b. We flush all fault queues on unbind() before freeing the PASID.
> + *
> + * So even though the Stop Marker might be issued by the device *after* the stop
> + * request completes, outstanding faults will have been dealt with by the time
> + * we free the PASID.
> + *
>    * Return: 0 on success and <0 on error.
>    */
>   int iommu_queue_iopf(struct iommu_fault *fault, void *cookie)
> 

The same for the comments.

Best regards,
baolu