Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 5.4 33/38] s390/mm: fix set_huge_pte_at() for empty ptes | Date | Fri, 5 Jun 2020 16:15:16 +0200 |
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From: Gerald Schaefer <gerald.schaefer@de.ibm.com>
[ Upstream commit ac8372f3b4e41015549b331a4f350224661e7fc6 ]
On s390, the layout of normal and large ptes (i.e. pmds/puds) differs. Therefore, set_huge_pte_at() does a conversion from a normal pte to the corresponding large pmd/pud. So, when converting an empty pte, this should result in an empty pmd/pud, which would return true for pmd/pud_none().
However, after conversion we also mark the pmd/pud as large, and therefore present. For empty ptes, this will result in an empty pmd/pud that is also marked as large, and pmd/pud_none() would not return true.
There is currently no issue with this behaviour, as set_huge_pte_at() does not seem to be called for empty ptes. It would be valid though, so let's fix this by not marking empty ptes as large in set_huge_pte_at().
This was found by testing a patch from from Anshuman Khandual, which is currently discussed on LKML ("mm/debug: Add more arch page table helper tests").
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Sasha Levin <sashal@kernel.org> --- arch/s390/mm/hugetlbpage.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/s390/mm/hugetlbpage.c b/arch/s390/mm/hugetlbpage.c index 5674710a4841..7dfae86afa47 100644 --- a/arch/s390/mm/hugetlbpage.c +++ b/arch/s390/mm/hugetlbpage.c @@ -159,10 +159,13 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr, rste &= ~_SEGMENT_ENTRY_NOEXEC; /* Set correct table type for 2G hugepages */ - if ((pte_val(*ptep) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3) - rste |= _REGION_ENTRY_TYPE_R3 | _REGION3_ENTRY_LARGE; - else + if ((pte_val(*ptep) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3) { + if (likely(pte_present(pte))) + rste |= _REGION3_ENTRY_LARGE; + rste |= _REGION_ENTRY_TYPE_R3; + } else if (likely(pte_present(pte))) rste |= _SEGMENT_ENTRY_LARGE; + clear_huge_pte_skeys(mm, rste); pte_val(*ptep) = rste; } -- 2.25.1
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