[PATCH v3 1/3] vfio/type1: Support faulting PFNMAP vmas

[Alex Williamson]

With conversion to follow_pfn(), DMA mapping a PFNMAP range depends on
the range being faulted into the vma.  Add support to manually provide
that, in the same way as done on KVM with hva_to_pfn_remapped().

Reviewed-by: Peter Xu <pet...@redhat.com>
Signed-off-by: Alex Williamson <alex.william...@redhat.com>
---
 drivers/vfio/vfio_iommu_type1.c |   36 +++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index cc1d64765ce7..4a4cb7cd86b2 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -317,6 +317,32 @@ static int put_pfn(unsigned long pfn, int prot)
        return 0;
 }
 
+static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
+                           unsigned long vaddr, unsigned long *pfn,
+                           bool write_fault)
+{
+       int ret;
+
+       ret = follow_pfn(vma, vaddr, pfn);
+       if (ret) {
+               bool unlocked = false;
+
+               ret = fixup_user_fault(NULL, mm, vaddr,
+                                      FAULT_FLAG_REMOTE |
+                                      (write_fault ?  FAULT_FLAG_WRITE : 0),
+                                      &unlocked);
+               if (unlocked)
+                       return -EAGAIN;
+
+               if (ret)
+                       return ret;
+
+               ret = follow_pfn(vma, vaddr, pfn);
+       }
+
+       return ret;
+}
+
 static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
                         int prot, unsigned long *pfn)
 {
@@ -339,12 +365,16 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned 
long vaddr,
 
        vaddr = untagged_addr(vaddr);
 
+retry:
        vma = find_vma_intersection(mm, vaddr, vaddr + 1);
 
        if (vma && vma->vm_flags & VM_PFNMAP) {
-               if (!follow_pfn(vma, vaddr, pfn) &&
-                   is_invalid_reserved_pfn(*pfn))
-                       ret = 0;
+               ret = follow_fault_pfn(vma, mm, vaddr, pfn, prot & IOMMU_WRITE);
+               if (ret == -EAGAIN)
+                       goto retry;
+
+               if (!ret && !is_invalid_reserved_pfn(*pfn))
+                       ret = -EFAULT;
        }
 done:
        up_read(&mm->mmap_sem);