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

On 02/09/2018 12:59 AM, Ram Pai wrote:

On Thu, Feb 08, 2018 at 08:46:27PM +0530, Aneesh Kumar K.V wrote:

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.

this fix may not be needed. It random corruption may be artifact of the typo you
had in your first patch?

Why? the tables at level 2 and leve3 are of different size and we should 
use the right offset to store the slot details. Even with the change you 
mentioned in the previous mail, I still have kernel crashes with 
hugetlbfs test running in parallel to a kernel build.

-aneesh