2014-12-10 18:01:20

by Christophe Leroy

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

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 <[email protected]>

---
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

2014-12-11 00:07:29

by Scott Wood

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

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