On Fri, 18 Oct 2019 14:42:32 +0800
Ben Luo <luo...@linux.alibaba.com> wrote:
> A friendly reminder :)
>
Thanks Ben! I've added this to the vfio next branch for v5.5 with
Andrea's R-b. Thanks,
Alex
> 在 2019/10/4 上午12:41, Andrea Arcangeli 写道:
> > On Thu, Oct 03, 2019 at 11:49:42AM +0800, Ben Luo wrote:
> >> Currently, no hugepage split code can transfer the reserved bit
> >> from head to tail during the split, so checking the head can't make
> >> a difference in a racing condition with hugepage spliting.
> >>
> >> The buddy wouldn't allow a driver to allocate an hugepage if any
> >> subpage is reserved in the e820 map at boot, if any driver sets the
> >> reserved bit of head page before mapping the hugepage in userland,
> >> it needs to set the reserved bit in all subpages to be safe.
> >>
> >> Signed-off-by: Ben Luo <luo...@linux.alibaba.com>
> > Reviewed-by: Andrea Arcangeli <aarca...@redhat.com>
> >
> >
> >> ---
> >> drivers/vfio/vfio_iommu_type1.c | 26 ++++----------------------
> >> 1 file changed, 4 insertions(+), 22 deletions(-)
> >>
> >> diff --git a/drivers/vfio/vfio_iommu_type1.c
> >> b/drivers/vfio/vfio_iommu_type1.c
> >> index 054391f..e2019ba 100644
> >> --- a/drivers/vfio/vfio_iommu_type1.c
> >> +++ b/drivers/vfio/vfio_iommu_type1.c
> >> @@ -287,31 +287,13 @@ static int vfio_lock_acct(struct vfio_dma *dma, long
> >> npage, bool async)
> >> * Some mappings aren't backed by a struct page, for example an mmap'd
> >> * MMIO range for our own or another device. These use a different
> >> * pfn conversion and shouldn't be tracked as locked pages.
> >> + * For compound pages, any driver that sets the reserved bit in head
> >> + * page needs to set the reserved bit in all subpages to be safe.
> >> */
> >> static bool is_invalid_reserved_pfn(unsigned long pfn)
> >> {
> >> - if (pfn_valid(pfn)) {
> >> - bool reserved;
> >> - struct page *tail = pfn_to_page(pfn);
> >> - struct page *head = compound_head(tail);
> >> - reserved = !!(PageReserved(head));
> >> - if (head != tail) {
> >> - /*
> >> - * "head" is not a dangling pointer
> >> - * (compound_head takes care of that)
> >> - * but the hugepage may have been split
> >> - * from under us (and we may not hold a
> >> - * reference count on the head page so it can
> >> - * be reused before we run PageReferenced), so
> >> - * we've to check PageTail before returning
> >> - * what we just read.
> >> - */
> >> - smp_rmb();
> >> - if (PageTail(tail))
> >> - return reserved;
> >> - }
> >> - return PageReserved(tail);
> >> - }
> >> + if (pfn_valid(pfn))
> >> + return PageReserved(pfn_to_page(pfn));
> >>
> >> return true;
> >> }
> >> --
> >> 1.8.3.1
> >>
