[PATCH 2/4] powerpc32: properly clear page table when 0 is not a good default PTE value

[PATCH 2/4] powerpc32: properly clear page table when 0 is not a good default PTE value

[Christophe Leroy]

Some HW invert some PTE bits. In some case, __pte(0) is not 0 so the PTEs shall
be properly set prior to being used.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

---
 arch/powerpc/mm/pgtable_32.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index a349089..71a2821 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -96,6 +96,14 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd)
 #endif
 }
 
+static inline void pte_alloc_clear(pte_t *pte)
+{
+	int i;
+
+	for (i = 0; i < PTRS_PER_PTE; i++)
+		pte[i] = __pte(0);
+}
+
 __init_refok pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
 {
 	pte_t *pte;
@@ -109,18 +117,24 @@ __init_refok pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long add
 		if (pte)
 			clear_page(pte);
 	}
+	if (pte && !pte_none(*pte))
+		pte_alloc_clear(pte);
 	return pte;
 }
 
 pgtable_t pte_alloc_one(struct mm_struct *mm, unsigned long address)
 {
 	struct page *ptepage;
+	pte_t *pte;
 
 	gfp_t flags = GFP_KERNEL | __GFP_REPEAT | __GFP_ZERO;
 
 	ptepage = alloc_pages(flags, 0);
 	if (!ptepage)
 		return NULL;
+	pte = (pte_t *)pfn_to_kaddr(page_to_pfn(ptepage));
+	if (!pte_none(*pte))
+		pte_alloc_clear(pte);
 	if (!pgtable_page_ctor(ptepage)) {
 		__free_page(ptepage);
 		return NULL;
-- 
2.1.0

Re: [PATCH 2/4] powerpc32: properly clear page table when 0 is not a good default PTE value

[Scott Wood]

On Wed, 2014-12-10 at 19:00 +0100, Christophe Leroy wrote:
> Some HW invert some PTE bits. In some case, __pte(0) is not 0 so the PTEs shall
> be properly set prior to being used.

__pte(0) is always zero.  If that changes in a future patch, that patch
is not doing the right thing.  The __pte()/pte_val() accesors should not
do anything beyond boxing/unboxing the value in a struct.  The right
place for special 8xx handling of the inverted bit is in pte_mkwrite()
and such.

I don't see any other architecture using __pte()/pte_val() this way.

-Scott