When a recoverable page fault is handled by the fault workqueue, find the
associated process and call handle_mm_fault.
In theory, we don't even need to take a reference to the iommu_process,
because any release of the structure is preceded by a flush of the queue.
I don't feel comfortable removing the pinning at the moment, though.
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
---
drivers/iommu/io-pgfault.c | 83 ++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 81 insertions(+), 2 deletions(-)
diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
index f31bc24534b0..532bdb9ce519 100644
--- a/drivers/iommu/io-pgfault.c
+++ b/drivers/iommu/io-pgfault.c
@@ -21,6 +21,7 @@
#include <linux/iommu.h>
#include <linux/list.h>
+#include <linux/sched/mm.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
@@ -83,8 +84,86 @@ static int iommu_fault_finish(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;
+ struct iommu_process *process;
+ int ret = IOMMU_FAULT_STATUS_INVALID;
+ unsigned int access_flags = 0;
+ unsigned int fault_flags = FAULT_FLAG_REMOTE;
+ struct iommu_fault *params = &fault->params;
+
+ if (!(params->flags & IOMMU_FAULT_PASID))
+ return ret;
+
+ process = iommu_process_find(params->pasid);
+ if (!process)
+ return ret;
+
+ if ((params->flags & (IOMMU_FAULT_LAST | IOMMU_FAULT_READ |
+ IOMMU_FAULT_WRITE)) == IOMMU_FAULT_LAST) {
+ /* Special case: PASID Stop Marker doesn't require a response */
+ ret = IOMMU_FAULT_STATUS_IGNORE;
+ goto out_put_process;
+ }
+
+ mm = process->mm;
+ if (!mmget_not_zero(mm)) {
+ /* Process is dead */
+ goto out_put_process;
+ }
+
+ down_read(&mm->mmap_sem);
+
+ vma = find_extend_vma(mm, params->address);
+ if (!vma)
+ /* Unmapped area */
+ goto out_put_mm;
+
+ if (params->flags & IOMMU_FAULT_READ)
+ access_flags |= VM_READ;
+
+ if (params->flags & IOMMU_FAULT_WRITE) {
+ access_flags |= VM_WRITE;
+ fault_flags |= FAULT_FLAG_WRITE;
+ }
+
+ if (params->flags & IOMMU_FAULT_EXEC) {
+ access_flags |= VM_EXEC;
+ fault_flags |= FAULT_FLAG_INSTRUCTION;
+ }
+
+ if (!(params->flags & 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, params->address, fault_flags);
+ ret = ret & VM_FAULT_ERROR ? IOMMU_FAULT_STATUS_INVALID :
+ IOMMU_FAULT_STATUS_HANDLED;
+
+out_put_mm:
+ up_read(&mm->mmap_sem);
+
+ /*
+ * Here's a fun scenario: the process exits while we're handling the
+ * fault on its mm. Since we're the last mm_user, mmput will call
+ * mm_exit immediately. exit_mm releases the mmu notifier, which calls
+ * iommu_notifier_release, which has to flush the fault queue that we're
+ * executing on... It's actually easy to reproduce with a DMA engine,
+ * and I did observe a lockdep splat. Therefore move the release of the
+ * mm to another thread, if we're the last user.
+ *
+ * mmput_async was removed in 4.14, and added back in 4.15(?)
+ * https://patchwork.kernel.org/patch/9952257/
+ */
+ mmput_async(mm);
+
+out_put_process:
+ iommu_process_put(process);
+
+ return ret;
}
static void iommu_fault_handle_group(struct work_struct *work)
--
2.13.3
--
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