[PATCH v2] powerpc/hugetlb: Fix 8M hugepages on 8xx

[PATCH v2] powerpc/hugetlb: Fix 8M hugepages on 8xx

[Christophe Leroy]

With HW assistance all page tables must be 4k aligned, the 8xx
drops the last 12 bits during the walk.

Redefine HUGEPD_SHIFT_MASK to mask last 12 bits out.
HUGEPD_SHIFT_MASK is used to for alignment of page table cache.

Fixes: 22569b881d37 ("powerpc/8xx: Enable 8M hugepage support with HW assistance")
Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
v2: Only do the fix of alignment which is the only vital fix.
---
 arch/powerpc/include/asm/page.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
index 86332080399a..080a0bf8e54b 100644
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -295,8 +295,13 @@ static inline bool pfn_valid(unsigned long pfn)
 /*
  * Some number of bits at the level of the page table that points to
  * a hugepte are used to encode the size.  This masks those bits.
+ * On 8xx, HW assistance requires 4k alignment for the hugepte.
  */
+#ifdef CONFIG_PPC_8xx
+#define HUGEPD_SHIFT_MASK     0xfff
+#else
 #define HUGEPD_SHIFT_MASK     0x3f
+#endif
 
 #ifndef __ASSEMBLY__
 
-- 
2.25.0

Re: [PATCH v2] powerpc/hugetlb: Fix 8M hugepages on 8xx

[Michael Ellerman]

On Sun, 2020-02-09 at 16:02:41 UTC, Christophe Leroy wrote:
> With HW assistance all page tables must be 4k aligned, the 8xx
> drops the last 12 bits during the walk.
> 
> Redefine HUGEPD_SHIFT_MASK to mask last 12 bits out.
> HUGEPD_SHIFT_MASK is used to for alignment of page table cache.
> 
> Fixes: 22569b881d37 ("powerpc/8xx: Enable 8M hugepage support with HW assistance")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/50a175dd18de7a647e72aca7daf4744e3a5a81e3

cheers