linux-kernel - [PATCH v4.14.y 1/3] vfio/type1: Support faulting PFNMAP vmas

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Date:   Tue, 8 Sep 2020 01:47:05 +0530
From:   Ajay Kaher <akaher@...are.com>
To:     <gregkh@...uxfoundation.org>, <sashal@...nel.org>
CC:     <alex.williamson@...hat.com>, <cohuck@...hat.com>,
        <peterx@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        <srivatsab@...are.com>, <srivatsa@...il.mit.edu>,
        <vsirnapalli@...are.com>, <akaher@...are.com>
Subject: [PATCH v4.14.y 1/3] vfio/type1: Support faulting PFNMAP vmas

From: Alex Williamson <alex.williamson@...hat.com>

commit 41311242221e3482b20bfed10fa4d9db98d87016 upstream.

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 <peterx@...hat.com>
Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
[Ajay: Regenerated the patch for v4.14]
Signed-off-by: Ajay Kaher <akaher@...are.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 35a3750..150be10 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -336,6 +336,32 @@ 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)
 {
@@ -375,12 +401,16 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
 
 	down_read(&mm->mmap_sem);
 
+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;
 	}
 
 	up_read(&mm->mmap_sem);
-- 
2.7.4