Re: [PATCH] powerpc: Avoid panic during boot due to divide by zero in init_cache_info()

On Sun, 2017-03-05 at 11:25 +1100, Benjamin Herrenschmidt wrote:

On Sun, 2017-03-05 at 10:54 +1100, Anton Blanchard wrote:

quoted

From: Anton Blanchard <redacted>

I see a panic in early boot when building with a recent gcc
toolchain.
The issue is a divide by zero, which is undefined. Older toolchains
let us get away with it:

Maybe we should panic though ... not having a valid cache block size
is going to be fatal in other areas...

 ... Unless it's for L2/L3 caches. Of course...

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

quoted

int foo(int a) { return a / 0; }

foo:
	li 9,0
	divw 3,3,9
	extsw 3,3
	blr

But newer ones catch it:

foo:
	trap

Add a check to avoid the divide by zero.

Fixes: bd067f83b084 ("powerpc/64: Fix naming of cache block vs.
cache
line")
Signed-off-by: Anton Blanchard <redacted>
---
 arch/powerpc/kernel/setup_64.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/setup_64.c

b/arch/powerpc/kernel/setup_64.c
index adf2084..afd1c26 100644

--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c

@@ -408,7 +408,8 @@ static void init_cache_info(struct

ppc_cache_info
*info, u32 size, u32 lsize,
 	info->line_size = lsize;
 	info->block_size = bsize;
 	info->log_block_size = __ilog2(bsize);
-	info->blocks_per_page = PAGE_SIZE / bsize;
+	if (bsize)
+		info->blocks_per_page = PAGE_SIZE / bsize;
 
 	if (sets == 0)
 		info->assoc = 0xffff;