Re: [PATCH RFC 03/13] mm/gup: Check p4d presence before going on
flat view
From: Jason Gunthorpe <jgg@nvidia.com>
Date: 2024-03-07 20:08:33
Also in:
linux-mm, linuxppc-dev, lkml, sparclinux
On Wed, Mar 06, 2024 at 06:41:37PM +0800, peterx@redhat.com wrote:
From: Peter Xu <peterx@redhat.com> Currently there should have no p4d swap entries so it may not matter much, however this may help us to rule out swap entries in pXd_huge() API, which will include p4d_huge(). The p4d_present() checks make it 100% clear that we won't rely on p4d_huge() for swap entries. Signed-off-by: Peter Xu <peterx@redhat.com> --- mm/gup.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
quoted hunk ↗ jump to hunk
p4dp = p4d_offset(pgdp, address); p4d = READ_ONCE(*p4dp); - if (p4d_none(p4d)) + if (p4d_none(p4d) || !p4d_present(p4d)) return no_page_table(vma, flags);
Like the other place I think this makes more sense as
if (!p4_present(p4d))
return no_page_table(vma, flags);
Since none can never be present.
IOW if the following code doesn't decode swap entries then it should
be guarded with a chceck on present not none..
Jason
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