Subject: [PATCH for-stable-v4.4 52/53] ARM: ensure that processor vtables is not lost after boot

From: Ard Biesheuvel <[email-masked]>
Date: Tue, 5 Nov 2019 21:58:45 +0100

From: Russell King <[email-masked]>

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 <[email-masked]>
Tested-by: Krzysztof Kozlowski <[email-masked]>
Fixes: 383fb3ee8024 ("ARM: spectre-v2: per-CPU vtables to work around big.Little systems")
Signed-off-by: Russell King <[email-masked]>
Signed-off-by: David A. Long <[email-masked]>
Reviewed-by: Julien Thierry <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
Signed-off-by: Ard Biesheuvel <[email-masked]>
---
 arch/arm/mm/proc-macros.S | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index 212147c78f4b..d36a283b4099 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -259,6 +259,13 @@
 	.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)
@@ -294,6 +301,9 @@ 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
-- 
2.17.1

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