[PATCH] powerpc/64s: Fix boot failure with 4K Radix

[PATCH] powerpc/64s: Fix boot failure with 4K Radix

[Michael Ellerman]

When using the Radix MMU our PGD is always 64K, and must be naturally
aligned.

For a 4K page size kernel that means page alignment of swapper_pg_dir is
not sufficient, leading to failure to boot.

Use the existing MAX_PTRS_PER_PGD which has the correct value, and
avoids us hard-coding 64K here.

Fixes: e72421a085a8 ("powerpc: Define swapper_pg_dir[] in C")
Reported-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/mm/pgtable.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index 1707ab580ee2..cd16b407f47e 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -28,7 +28,13 @@
 #include <asm/hugetlb.h>
 #include <asm/pte-walk.h>
 
-pgd_t swapper_pg_dir[MAX_PTRS_PER_PGD] __page_aligned_bss;
+#ifdef CONFIG_PPC64
+#define PGD_ALIGN (sizeof(pgd_t) * MAX_PTRS_PER_PGD)
+#else
+#define PGD_ALIGN PAGE_SIZE
+#endif
+
+pgd_t swapper_pg_dir[MAX_PTRS_PER_PGD] __section(".bss..page_aligned") __aligned(PGD_ALIGN);
 
 static inline int is_exec_fault(void)
 {
-- 
2.25.1

Re: [PATCH] powerpc/64s: Fix boot failure with 4K Radix

[Michael Ellerman]

On Thu, 24 Jun 2021 22:34:20 +1000, Michael Ellerman wrote:
> When using the Radix MMU our PGD is always 64K, and must be naturally
> aligned.
> 
> For a 4K page size kernel that means page alignment of swapper_pg_dir is
> not sufficient, leading to failure to boot.
> 
> Use the existing MAX_PTRS_PER_PGD which has the correct value, and
> avoids us hard-coding 64K here.

Applied to powerpc/next.

[1/1] powerpc/64s: Fix boot failure with 4K Radix
      https://git.kernel.org/powerpc/c/3018fbc63632e6d30abde228f29aaeaf78b782bf

cheers