linux-kernel - [PATCH 4.14 08/53] vfio: Use get_user_pages

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Date:   Tue, 10 Jul 2018 20:24:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jason Gunthorpe <jgg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: [PATCH 4.14 08/53] vfio: Use get_user_pages_longterm correctly

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Gunthorpe <jgg@...lanox.com>

commit bb94b55af3461e26b32f0e23d455abeae0cfca5d upstream.

The patch noted in the fixes below converted get_user_pages_fast() to
get_user_pages_longterm(), however the two calls differ in a few ways.

First _fast() is documented to not require the mmap_sem, while _longterm()
is documented to need it. Hold the mmap sem as required.

Second, _fast accepts an 'int write' while _longterm uses 'unsigned int
gup_flags', so the expression '!!(prot & IOMMU_WRITE)' is only working by
luck as FOLL_WRITE is currently == 0x1. Use the expected FOLL_WRITE
constant instead.

Fixes: 94db151dc892 ("vfio: disable filesystem-dax page pinning")
Cc: <stable@...r.kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@...lanox.com>
Acked-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/vfio/vfio_iommu_type1.c |   16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -339,18 +339,16 @@ static int vaddr_get_pfn(struct mm_struc
 	struct page *page[1];
 	struct vm_area_struct *vma;
 	struct vm_area_struct *vmas[1];
+	unsigned int flags = 0;
 	int ret;
 
+	if (prot & IOMMU_WRITE)
+		flags |= FOLL_WRITE;
+
+	down_read(&mm->mmap_sem);
 	if (mm == current->mm) {
-		ret = get_user_pages_longterm(vaddr, 1, !!(prot & IOMMU_WRITE),
-					      page, vmas);
+		ret = get_user_pages_longterm(vaddr, 1, flags, page, vmas);
 	} else {
-		unsigned int flags = 0;
-
-		if (prot & IOMMU_WRITE)
-			flags |= FOLL_WRITE;
-
-		down_read(&mm->mmap_sem);
 		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
 					    vmas, NULL);
 		/*
@@ -364,8 +362,8 @@ static int vaddr_get_pfn(struct mm_struc
 			ret = -EOPNOTSUPP;
 			put_page(page[0]);
 		}
-		up_read(&mm->mmap_sem);
 	}
+	up_read(&mm->mmap_sem);
 
 	if (ret == 1) {
 		*pfn = page_to_pfn(page[0]);