[PATCH 1/2] powerpc/strict_rwx: quirks for STRICT_RWX patches

[Balbir Singh <bsingharora@gmail.com>]

This patch disables STRICT_RWX for power9 DD1 machines
where due to some limitations with the way we do tlb
updates, we clear the TLB entry of the text that's doing
the update to kernel text and that does lead to a
crash.

Fixes: 7614ff3 ("powerpc/mm/radix: Implement STRICT_RWX/mark_rodata_ro() for Radix")

Cc: stable@vger.kernel.org

Reported-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
---
 arch/powerpc/mm/pgtable-radix.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
index 39c252b..c2a2b46 100644
--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -169,6 +169,18 @@ void radix__mark_rodata_ro(void)
 {
 	unsigned long start, end;
 
+	/*
+	 * mark_rodata_ro() will mark itself as !writable at some point
+	 * due to workaround in radix__pte_update(), we'll end up with
+	 * an invalid pte and the system will crash quite severly.
+	 * The alternatives are quite cumbersome and leaving out
+	 * the page containing the flush code is not very nice.
+	 */
+	if (cpu_has_feature(CPU_FTR_POWER9_DD1)) {
+		pr_warn("Warning: Unable to mark rodata read only on P9 DD1\n");
+		return;
+	}
+
 	start = (unsigned long)_stext;
 	end = (unsigned long)__init_begin;
 
-- 
2.9.5