arm64: Allow CAVIUM_TX2_ERRATUM_219 to be selected

Allow the user to select the workaround for TX2-219, and update
the silicon-errata.rst file to reflect this.

Cc: <stable@vger.kernel.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

Documentation/arm64/silicon-errata.rst

@@ -107,6 +107,8 @@ stable kernels.
 +----------------+-----------------+-----------------+-----------------------------+
 | Cavium         | ThunderX2 SMMUv3| #126            | N/A                         |
 +----------------+-----------------+-----------------+-----------------------------+
+| Cavium         | ThunderX2 Core  | #219            | CAVIUM_TX2_ERRATUM_219      |
++----------------+-----------------+-----------------+-----------------------------+
 +----------------+-----------------+-----------------+-----------------------------+
 | Freescale/NXP  | LS2080A/LS1043A | A-008585        | FSL_ERRATUM_A008585         |
 +----------------+-----------------+-----------------+-----------------------------+

arch/arm64/Kconfig

@@ -617,6 +617,23 @@ config CAVIUM_ERRATUM_30115
 
 	  If unsure, say Y.
 
+config CAVIUM_TX2_ERRATUM_219
+	bool "Cavium ThunderX2 erratum 219: PRFM between TTBR change and ISB fails"
+	default y
+	help
+	  On Cavium ThunderX2, a load, store or prefetch instruction between a
+	  TTBR update and the corresponding context synchronizing operation can
+	  cause a spurious Data Abort to be delivered to any hardware thread in
+	  the CPU core.
+
+	  Work around the issue by avoiding the problematic code sequence and
+	  trapping KVM guest TTBRx_EL1 writes to EL2 when SMT is enabled. The
+	  trap handler performs the corresponding register access, skips the
+	  instruction and ensures context synchronization by virtue of the
+	  exception return.
+
+	  If unsure, say Y.
+
 config QCOM_FALKOR_ERRATUM_1003
 	bool "Falkor E1003: Incorrect translation due to ASID change"
 	default y