Commit bb94b55a authored Jun 29, 2018 by Jason Gunthorpe Committed by Alex Williamson Jun 30, 2018

vfio: Use get_user_pages_longterm correctly



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: 94db151d ("vfio: disable filesystem-dax page pinning")
Cc: <stable@vger.kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

parent 7733e05b

drivers/vfio/vfio_iommu_type1.c

+7 −9

Original line number	Diff line number	Diff line
		@@ -343,18 +343,16 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
		struct page *page[1];
		struct vm_area_struct *vma;
		struct vm_area_struct *vmas[1];
		int ret;

		if (mm == current->mm) {
		ret = get_user_pages_longterm(vaddr, 1, !!(prot & IOMMU_WRITE),
		page, vmas);
		} else {
		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, flags, page, vmas);
		} else {
		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
		vmas, NULL);
		/*
		@@ -368,8 +366,8 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
		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]);