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

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> writes:

> "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> writes:
>
>> 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 <aneesh.kumar@linux.vnet.ibm.com>
>
> 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 <aneesh.kumar@linux.vnet.ibm.com>
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.
    
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
The other option is to get huget_pte_get_and_clear to clear the second half of the page table.
That requires generic changes, because we don't have hugetlb page size available there.

diff --git a/arch/powerpc/include/asm/book3s/64/pgalloc.h b/arch/powerpc/include/asm/book3s/64/pgalloc.h
index 53df86d3cfce..adb7fba4b6c7 100644
--- a/arch/powerpc/include/asm/book3s/64/pgalloc.h
+++ b/arch/powerpc/include/asm/book3s/64/pgalloc.h
@@ -73,10 +73,13 @@ static inline void radix__pgd_free(struct mm_struct *mm, pgd_t *pgd)
 
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
+	pgd_t *pgd;
 	if (radix_enabled())
 		return radix__pgd_alloc(mm);
-	return kmem_cache_alloc(PGT_CACHE(PGD_INDEX_SIZE),
-		pgtable_gfp_flags(mm, GFP_KERNEL));
+	pgd = kmem_cache_alloc(PGT_CACHE(PGD_INDEX_SIZE),
+			       pgtable_gfp_flags(mm, GFP_KERNEL));
+	memset(pgd, 0, PGD_TABLE_SIZE);
+	return pgd;
 }
 
 static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
@@ -93,8 +96,11 @@ static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, pud_t *pud)
 
 static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr)
 {
-	return kmem_cache_alloc(PGT_CACHE(PUD_CACHE_INDEX),
-		pgtable_gfp_flags(mm, GFP_KERNEL));
+	pud_t *pud;
+	pud = kmem_cache_alloc(PGT_CACHE(PUD_CACHE_INDEX),
+			       pgtable_gfp_flags(mm, GFP_KERNEL));
+	memset(pud, 0, PUD_TABLE_SIZE);
+	return pud;
 }
 
 static inline void pud_free(struct mm_struct *mm, pud_t *pud)