ARM: ensure that processor vtables is not lost after boot

Commit 3a4d0c2172bcf15b7a3d9d498b2b355f9864286b upstream.

Marek Szyprowski reported problems with CPU hotplug in current kernels.
This was tracked down to the processor vtables being located in an
init section, and therefore discarded after kernel boot, despite being
required after boot to properly initialise the non-boot CPUs.

Arrange for these tables to end up in .rodata when required.

Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Krzysztof Kozlowski <krzk@kernel.org>
Fixes: 383fb3ee8024 ("ARM: spectre-v2: per-CPU vtables to work around big.Little systems")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David A. Long <dave.long@linaro.org>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Tested-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index 81d0efb055c66080e976f9504c69866f7699b1a6..19516fbc2c55a65c761094bf3a67c8cd69568183 100644 (file)
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -274,6 +274,13 @@
        .endm
 
 .macro define_processor_functions name:req, dabort:req, pabort:req, nommu=0, suspend=0, bugs=0
+/*
+ * If we are building for big.Little with branch predictor hardening,
+ * we need the processor function tables to remain available after boot.
+ */
+#if 1 // defined(CONFIG_BIG_LITTLE) && defined(CONFIG_HARDEN_BRANCH_PREDICTOR)
+       .section ".rodata"
+#endif
        .type   \name\()_processor_functions, #object
        .align 2
 ENTRY(\name\()_processor_functions)
@@ -309,6 +316,9 @@ ENTRY(\name\()_processor_functions)
        .endif
 
        .size   \name\()_processor_functions, . - \name\()_processor_functions
+#if 1 // defined(CONFIG_BIG_LITTLE) && defined(CONFIG_HARDEN_BRANCH_PREDICTOR)
+       .previous
+#endif
 .endm
 
 .macro define_cache_functions name:req