arm64: errata: Unify speculative SSBS errata logic

Cortex-X4 erratum 3194386 and Neoverse-V3 erratum 3312417 are identical,
with duplicate Kconfig text and some unsightly ifdeffery. While we try
to share code behind CONFIG_ARM64_WORKAROUND_SPECULATIVE_SSBS, having
separate options results in a fair amount of boilerplate code, and this
will only get worse as we expand the set of affected CPUs.

To reduce this boilerplate, unify the two behind a common Kconfig
option. This removes the duplicate text and Kconfig logic, and removes
the need for the intermediate ARM64_WORKAROUND_SPECULATIVE_SSBS option.
The set of affected CPUs is described as a list so that this can easily
be extended.

I've used ARM64_ERRATUM_3194386 (matching the Neoverse-V3 erratum ID) as
the common option, matching the way we use ARM64_ERRATUM_1319367 to
cover Cortex-A57 erratum 1319537 and Cortex-A72 erratum 1319367.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <wilL@kernel.org>
Link: https://lore.kernel.org/r/20240603111812.1514101-5-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Documentation/arch/arm64/silicon-errata.rst

@@ -158,7 +158,7 @@ stable kernels.
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Neoverse-V1     | #1619801        | N/A                         |
 +----------------+-----------------+-----------------+-----------------------------+
-| ARM            | Neoverse-V3     | #3312417        | ARM64_ERRATUM_3312417       |
+| ARM            | Neoverse-V3     | #3312417        | ARM64_ERRATUM_3194386       |
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | MMU-500         | #841119,826419  | N/A                         |
 +----------------+-----------------+-----------------+-----------------------------+

arch/arm64/Kconfig

@@ -1067,15 +1067,14 @@ config ARM64_ERRATUM_3117295
 
 	  If unsure, say Y.
 
-config ARM64_WORKAROUND_SPECULATIVE_SSBS
-	bool
-
 config ARM64_ERRATUM_3194386
-	bool "Cortex-X4: 3194386: workaround for MSR SSBS not self-synchronizing"
+	bool "Cortex-X4/Neoverse-V3: workaround for MSR SSBS not self-synchronizing"
-	select ARM64_WORKAROUND_SPECULATIVE_SSBS
 	default y
 	help
-	  This option adds the workaround for ARM Cortex-X4 erratum 3194386.
+	  This option adds the workaround for the following errata:
+
+	  * ARM Cortex-X4 erratum 3194386
+	  * ARM Neoverse-V3 erratum 3312417
 
 	  On affected cores "MSR SSBS, #0" instructions may not affect
 	  subsequent speculative instructions, which may permit unexepected
@@ -1089,26 +1088,6 @@ config ARM64_ERRATUM_3194386
 
 	  If unsure, say Y.
 
-config ARM64_ERRATUM_3312417
-	bool "Neoverse-V3: 3312417: workaround for MSR SSBS not self-synchronizing"
-	select ARM64_WORKAROUND_SPECULATIVE_SSBS
-	default y
-	help
-	  This option adds the workaround for ARM Neoverse-V3 erratum 3312417.
-
-	  On affected cores "MSR SSBS, #0" instructions may not affect
-	  subsequent speculative instructions, which may permit unexepected
-	  speculative store bypassing.
-
-	  Work around this problem by placing a speculation barrier after
-	  kernel changes to SSBS. The presence of the SSBS special-purpose
-	  register is hidden from hwcaps and EL0 reads of ID_AA64PFR1_EL1, such
-	  that userspace will use the PR_SPEC_STORE_BYPASS prctl to change
-	  SSBS.
-
-	  If unsure, say Y.
-
-
 config CAVIUM_ERRATUM_22375
 	bool "Cavium erratum 22375, 24313"
 	default y

arch/arm64/include/asm/cpucaps.h

@@ -59,7 +59,7 @@ cpucap_is_possible(const unsigned int cap)
 	case ARM64_WORKAROUND_REPEAT_TLBI:
 		return IS_ENABLED(CONFIG_ARM64_WORKAROUND_REPEAT_TLBI);
 	case ARM64_WORKAROUND_SPECULATIVE_SSBS:
-		return IS_ENABLED(CONFIG_ARM64_WORKAROUND_SPECULATIVE_SSBS);
+		return IS_ENABLED(CONFIG_ARM64_ERRATUM_3194386);
 	}
 
 	return true;

arch/arm64/kernel/cpu_errata.c

@@ -432,14 +432,10 @@ static const struct midr_range erratum_spec_unpriv_load_list[] = {
 };
 #endif
 
-#ifdef CONFIG_ARM64_WORKAROUND_SPECULATIVE_SSBS
-static const struct midr_range erratum_spec_ssbs_list[] = {
 #ifdef CONFIG_ARM64_ERRATUM_3194386
+static const struct midr_range erratum_spec_ssbs_list[] = {
 	MIDR_ALL_VERSIONS(MIDR_CORTEX_X4),
-#endif
-#ifdef CONFIG_ARM64_ERRATUM_3312417
 	MIDR_ALL_VERSIONS(MIDR_NEOVERSE_V3),
-#endif
 	{}
 };
 #endif
@@ -741,7 +737,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		MIDR_FIXED(MIDR_CPU_VAR_REV(1,1), BIT(25)),
 	},
 #endif
-#ifdef CONFIG_ARM64_WORKAROUND_SPECULATIVE_SSBS
+#ifdef CONFIG_ARM64_ERRATUM_3194386
 	{
 		.desc = "ARM errata 3194386, 3312417",
 		.capability = ARM64_WORKAROUND_SPECULATIVE_SSBS,

arch/arm64/kernel/proton-pack.c

@@ -567,7 +567,7 @@ static enum mitigation_state spectre_v4_enable_hw_mitigation(void)
 	 * Mitigate this with an unconditional speculation barrier, as CPUs
 	 * could mis-speculate branches and bypass a conditional barrier.
 	 */
-	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_SPECULATIVE_SSBS))
+	if (IS_ENABLED(CONFIG_ARM64_ERRATUM_3194386))
 		spec_bar();
 
 	return SPECTRE_MITIGATED;