As for Spectre variant-2, we rely on SMCCC 1.1 to provide the
discovery mechanism for detecting the SSBD mitigation.

A new capability is also allocated for that purpose, and a
config option.

Signed-off-by: Marc Zyngier <redacted>
---
  arch/arm64/Kconfig               |  9 ++++++
  arch/arm64/include/asm/cpucaps.h |  3 +-
  arch/arm64/kernel/cpu_errata.c   | 69 ++++++++++++++++++++++++++++++++++++++++
  3 files changed, 80 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index eb2cf4938f6d..b2103b4df467 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -938,6 +938,15 @@ config HARDEN_EL2_VECTORS
  
  	  If unsure, say Y.
  
+config ARM64_SSBD
+	bool "Speculative Store Bypass Disable" if EXPERT
+	default y
+	help
+	  This enables mitigation of the bypassing of previous stores
+	  by speculative loads.
+
+	  If unsure, say Y.
+
  menuconfig ARMV8_DEPRECATED
  	bool "Emulate deprecated/obsolete ARMv8 instructions"
  	depends on COMPAT

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index bc51b72fafd4..5b2facf786ba 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h

@@ -48,7 +48,8 @@
  #define ARM64_HAS_CACHE_IDC			27
  #define ARM64_HAS_CACHE_DIC			28
  #define ARM64_HW_DBM				29
+#define ARM64_SSBD			30