Re: [PATCH 1/2] powerpc/mm: Fix crashes with PUD level hugetlb config

On 02/10/2018 10:20 PM, Ram Pai wrote:

On Sat, Feb 10, 2018 at 03:17:02PM +0530, Aneesh Kumar K.V wrote:

quoted

Aneesh Kumar K.V [off-list ref] writes:

quoted

"Aneesh Kumar K.V" [off-list ref] writes:

quoted

To support memory keys, we moved the hash pte slot information to the second
half of the page table. This was ok with PTE entries at level 4 and level 3.
We already allocate larger page table pages at those level to accomodate extra
details. For level 4 we already have the extra space which was used to track
4k hash page table entry details and at pmd level the extra space was allocated
to track the THP details.

With hugetlbfs PTE, we used this extra space at the PMD level to store the
slot details. But we also support hugetlbfs PTE at PUD leve and PUD level page
didn't allocate extra space. This resulted in memory corruption.

Fix this by allocating extra space at PUD level when HUGETLB is enabled. We
may need further changes to allocate larger space at PMD level when we enable
HUGETLB. That will be done in next patch.

Fixes:bf9a95f9a6481bc6e(" powerpc: Free up four 64K PTE bits in 64K backed HPTE pages")

Signed-off-by: Aneesh Kumar K.V <redacted>

Another fix, I still get random memory corruption with hugetlb test with
16G hugepage config.

Another one. I am not sure whether we really want this in this form. But
with this tests are running fine.

-aneesh

commit 658fe8c310a913e69e5bc9a40d4c28a3b88d5c08
Author: Aneesh Kumar K.V [off-list ref]
Date:   Sat Feb 10 13:17:34 2018 +0530

     powerpc/mm/hash64: memset the pagetable pages on allocation.
     
     Now that we are using second half of the table to store slot details and we
     don't clear them in the huge_pte_get_and_clear, we need to make sure we zero
     out the range on allocation. This done some extra work because the first half
     of the table is cleared by huge_pte_get_and_clear and memset in this patch
     zero-out the full table page.
     
     We need to do this for pgd and pud because both get allocated from the same slab
     cache.

Do we need to zero pgd aswell to resolve your corruption? pud is not
sufficient? Or was it done to avoid issues in the future in case pgd
is used as the leaf; possibly for Terra_huge_pages?

it is the other way round, we need to zero-out pgd. pud zerout can be 
optional because first half of the page table is always cleared in the 
unmap path.

-aneesh