arm64: Workaround for Cortex-A55 erratum 1530923

Cortex-A55 erratum 1530923 allows TLB entries to be allocated as a
result of a speculative AT instruction. This may happen in the middle of
a guest world switch while the relevant VMSA configuration is in an
inconsistent state, leading to erroneous content being allocated into
TLBs.

The same workaround as is used for Cortex-A76 erratum 1165522
(WORKAROUND_SPECULATIVE_AT_VHE) can be used here. Note that this
mandates the use of VHE on affected parts.

Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

Documentation/arm64/silicon-errata.rst

@@ -88,6 +88,8 @@ stable kernels.
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Cortex-A76      | #1463225        | ARM64_ERRATUM_1463225       |
 +----------------+-----------------+-----------------+-----------------------------+
+| ARM            | Cortex-A55      | #1530923        | ARM64_ERRATUM_1530923       |
++----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Neoverse-N1     | #1188873,1418040| ARM64_ERRATUM_1418040       |
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Neoverse-N1     | #1349291        | N/A                         |

arch/arm64/Kconfig

@@ -530,6 +530,19 @@ config ARM64_ERRATUM_1165522
 
 	  If unsure, say Y.
 
+config ARM64_ERRATUM_1530923
+	bool "Cortex-A55: Speculative AT instruction using out-of-context translation regime could cause subsequent request to generate an incorrect translation"
+	default y
+	select ARM64_WORKAROUND_SPECULATIVE_AT_VHE
+	help
+	  This option adds a workaround for ARM Cortex-A55 erratum 1530923.
+
+	  Affected Cortex-A55 cores (r0p0, r0p1, r1p0, r2p0) could end-up with
+	  corrupted TLBs by speculating an AT instruction during a guest
+	  context switch.
+
+	  If unsure, say Y.
+
 config ARM64_ERRATUM_1286807
 	bool "Cortex-A76: Modification of the translation table for a virtual address might lead to read-after-read ordering violation"
 	default y

arch/arm64/include/asm/kvm_hyp.h

@@ -91,8 +91,8 @@ static __always_inline void __hyp_text __load_guest_stage2(struct kvm *kvm)
 	write_sysreg(kvm_get_vttbr(kvm), vttbr_el2);
 
 	/*
-	 * ARM erratum 1165522 requires the actual execution of the above
-	 * before we can switch to the EL1/EL0 translation regime used by
+	 * ARM errata 1165522 and 1530923 require the actual execution of the
+	 * above before we can switch to the EL1/EL0 translation regime used by
 	 * the guest.
 	 */
 	asm(ALTERNATIVE("nop", "isb", ARM64_WORKAROUND_SPECULATIVE_AT_VHE));

arch/arm64/kernel/cpu_errata.c

@@ -762,6 +762,10 @@ static const struct midr_range erratum_speculative_at_vhe_list[] = {
 #ifdef CONFIG_ARM64_ERRATUM_1165522
 	/* Cortex A76 r0p0 to r2p0 */
 	MIDR_RANGE(MIDR_CORTEX_A76, 0, 0, 2, 0),
+#endif
+#ifdef CONFIG_ARM64_ERRATUM_1530923
+	/* Cortex A55 r0p0 to r2p0 */
+	MIDR_RANGE(MIDR_CORTEX_A55, 0, 0, 2, 0),
 #endif
 	{},
 };
@@ -895,7 +899,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 #endif
 #ifdef CONFIG_ARM64_WORKAROUND_SPECULATIVE_AT_VHE
 	{
-		.desc = "ARM erratum 1165522",
+		.desc = "ARM errata 1165522, 1530923",
 		.capability = ARM64_WORKAROUND_SPECULATIVE_AT_VHE,
 		ERRATA_MIDR_RANGE_LIST(erratum_speculative_at_vhe_list),
 	},

arch/arm64/kvm/hyp/switch.c

@@ -158,8 +158,8 @@ static void deactivate_traps_vhe(void)
 	write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
 
 	/*
-	 * ARM erratum 1165522 requires the actual execution of the above
-	 * before we can switch to the EL2/EL0 translation regime used by
+	 * ARM errata 1165522 and 1530923 require the actual execution of the
+	 * above before we can switch to the EL2/EL0 translation regime used by
 	 * the host.
 	 */
 	asm(ALTERNATIVE("nop", "isb", ARM64_WORKAROUND_SPECULATIVE_AT_VHE));

arch/arm64/kvm/hyp/tlb.c

@@ -25,8 +25,8 @@ static void __hyp_text __tlb_switch_to_guest_vhe(struct kvm *kvm,
 
 	if (cpus_have_const_cap(ARM64_WORKAROUND_SPECULATIVE_AT_VHE)) {
 		/*
-		 * For CPUs that are affected by ARM erratum 1165522, we
-		 * cannot trust stage-1 to be in a correct state at that
+		 * For CPUs that are affected by ARM errata 1165522 or 1530923,
+		 * we cannot trust stage-1 to be in a correct state at that
 		 * point. Since we do not want to force a full load of the
 		 * vcpu state, we prevent the EL1 page-table walker to
 		 * allocate new TLBs. This is done by setting the EPD bits