[PATCH 4.4 62/74] MIPS: scache: Fix scache init with invalid line size.

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Govindraj Raja <govindraj.raja@xxxxxxxxxx>

commit 56fa81fc9a5445938f3aa2e63d15ab63dc938ad6 upstream.

In current scache init cache line_size is determined from
cpu config register, however if there there no scache
then mips_sc_probe_cm3 function populates a invalid line_size of 2.

The invalid line_size can cause a NULL pointer deference
during r4k_dma_cache_inv as r4k_blast_scache is populated
based on line_size. Scache line_size of 2 is invalid option in
r4k_blast_scache_setup.

This issue was faced during a MIPS I6400 based virtual platform bring up
where scache was not available in virtual platform model.

Signed-off-by: Govindraj Raja <Govindraj.Raja@xxxxxxxxxx>
Fixes: 7d53e9c4cd21("MIPS: CM3: Add support for CM3 L2 cache.")
Cc: Paul Burton <paul.burton@xxxxxxxxxx>
Cc: James Hogan <james.hogan@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: James Hartley <James.Hartley@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/12710/
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/mips/mm/sc-mips.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--- a/arch/mips/mm/sc-mips.c
+++ b/arch/mips/mm/sc-mips.c
@@ -164,11 +164,13 @@ static int __init mips_sc_probe_cm3(void
 
 	sets = cfg & CM_GCR_L2_CONFIG_SET_SIZE_MSK;
 	sets >>= CM_GCR_L2_CONFIG_SET_SIZE_SHF;
-	c->scache.sets = 64 << sets;
+	if (sets)
+		c->scache.sets = 64 << sets;
 
 	line_sz = cfg & CM_GCR_L2_CONFIG_LINE_SIZE_MSK;
 	line_sz >>= CM_GCR_L2_CONFIG_LINE_SIZE_SHF;
-	c->scache.linesz = 2 << line_sz;
+	if (line_sz)
+		c->scache.linesz = 2 << line_sz;
 
 	assoc = cfg & CM_GCR_L2_CONFIG_ASSOC_MSK;
 	assoc >>= CM_GCR_L2_CONFIG_ASSOC_SHF;
@@ -176,9 +178,12 @@ static int __init mips_sc_probe_cm3(void
 	c->scache.waysize = c->scache.sets * c->scache.linesz;
 	c->scache.waybit = __ffs(c->scache.waysize);
 
-	c->scache.flags &= ~MIPS_CACHE_NOT_PRESENT;
+	if (c->scache.linesz) {
+		c->scache.flags &= ~MIPS_CACHE_NOT_PRESENT;
+		return 1;
+	}
 
-	return 1;
+	return 0;
 }
 
 void __weak platform_early_l2_init(void)