[PATCH 08/37] iommu/fault: Handle mm faults

[jacob.jun.pan@linux.intel.com (Jacob Pan)]

On Mon, 12 Feb 2018 18:33:23 +0000
Jean-Philippe Brucker <jean-philippe.brucker@arm.com> 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.brucker@arm.com>
> ---
>  drivers/iommu/io-pgfault.c | 89
> ++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 87
> insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
> index 33309ed316d2..565ec01a1b5f 100644
> --- a/drivers/iommu/io-pgfault.c
> +++ b/drivers/iommu/io-pgfault.c
> @@ -9,6 +9,7 @@
>  
>  #include <linux/iommu.h>
>  #include <linux/list.h>
> +#include <linux/sched/mm.h>
>  #include <linux/slab.h>
>  #include <linux/workqueue.h>
>  
> @@ -82,8 +83,92 @@ static int iommu_fault_complete(struct
> iommu_domain *domain, struct device *dev, 
>  static int iommu_fault_handle_single(struct iommu_fault_context
> *fault) {
> -	/* TODO */
> -	return -ENODEV;
> +	struct mm_struct *mm;
> +	struct vm_area_struct *vma;
> +	unsigned int access_flags = 0;
unsigned long to match vm_flags?
> +	int ret = IOMMU_PAGE_RESP_INVALID;
> +	unsigned int fault_flags = FAULT_FLAG_REMOTE;
> +	struct iommu_fault_event *evt = &fault->evt;
> +
> +	if (!evt->pasid_valid)
> +		return ret;
I guess for not we don't handle PRQ without PASID, right?
> +
> +	/*
> +	 * Special case: PASID Stop Marker (LRW = 0b100) doesn't
> expect a
> +	 * response. A Stop Marker may be generated when disabling a
> PASID
> +	 * (issuing a PASID stop request) in some PCI devices.
> +	 *
> +	 * When the mm_exit() callback returns from the device
> driver, 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.
> +	 *
> +	 * We ignore the Stop Marker because:
> +	 * a. Page requests, which are posted requests, have been
> flushed to the
> +	 *    IOMMU when mm_exit() returns,
> +	 * b. We flush all fault queues after mm_exit() returns and
> 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.
> +	 */
> +	if (evt->last_req &&
> +	    !(evt->prot & (IOMMU_FAULT_READ | IOMMU_FAULT_WRITE)))
> +		return IOMMU_PAGE_RESP_HANDLED;
> +
If we don't expect a page response, shouldn't it be filtered by the
IOMMU vendor driver in the first place? i.e. in the vendor IOMMU driver
PRQ handler, it will sanitize the request anyway, for anything that
does not need response, it will not call iommu_report_device_fault().
> +	mm = iommu_sva_find(evt->pasid);
> +	if (!mm)
> +		return ret;
> +
> +	down_read(&mm->mmap_sem);
> +
> +	vma = find_extend_vma(mm, evt->addr);
> +	if (!vma)
> +		/* Unmapped area */
> +		goto out_put_mm;
> +
> +	if (evt->prot & IOMMU_FAULT_READ)
> +		access_flags |= VM_READ;
> +
> +	if (evt->prot & IOMMU_FAULT_WRITE) {
> +		access_flags |= VM_WRITE;
> +		fault_flags |= FAULT_FLAG_WRITE;
> +	}
> +
> +	if (evt->prot & IOMMU_FAULT_EXEC) {
> +		access_flags |= VM_EXEC;
> +		fault_flags |= FAULT_FLAG_INSTRUCTION;
> +	}
> +
> +	if (!(evt->prot & IOMMU_FAULT_PRIV))
> +		fault_flags |= FAULT_FLAG_USER;
> +
> +	if (access_flags & ~vma->vm_flags)
> +		/* Access fault */
> +		goto out_put_mm;
> +
> +	ret = handle_mm_fault(vma, evt->addr, fault_flags);
> +	ret = ret & VM_FAULT_ERROR ? IOMMU_PAGE_RESP_INVALID :
> +		IOMMU_PAGE_RESP_SUCCESS;
> +
> +out_put_mm:
> +	up_read(&mm->mmap_sem);
> +
> +	/*
> +	 * If the process exits while we're handling the fault on
> its mm, we
> +	 * can't do mmput(). exit_mmap() would release the MMU
> notifier, calling
> +	 * iommu_notifier_release(), which has to flush the fault
> queue that
> +	 * we're executing on... So mmput_async() moves the release
> of the mm to
> +	 * another thread, if we're the last user.
> +	 */
> +	mmput_async(mm);
> +
> +	return ret;
>  }
>  
>  static void iommu_fault_handle_group(struct work_struct *work)

[Jacob Pan]