Revert "arm64: errata: Mitigate Ampere1 erratum AC03_CPU_38 at stage-2"

This reverts commit cde7f2fd63 which is
commit 6df696cd9bc1ceed0e92e36908f88bbd16d18255 upstream.

It breaks the Android abi and isn't really needed for Android systems.
If it is needed in the future, it can come back in an ABI-safe way.

Bug: 161946584
Change-Id: I5134a2ccd9bd11cb7fbf3e5c6d8a0f2b8ee924d3
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

Documentation/arm64/silicon-errata.rst

@@ -52,9 +52,6 @@ stable kernels.
 | Allwinner      | A64/R18         | UNKNOWN1        | SUN50I_ERRATUM_UNKNOWN1     |
 +----------------+-----------------+-----------------+-----------------------------+
 +----------------+-----------------+-----------------+-----------------------------+
-| Ampere         | AmpereOne       | AC03_CPU_38     | AMPERE_ERRATUM_AC03_CPU_38  |
-+----------------+-----------------+-----------------+-----------------------------+
-+----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Cortex-A510     | #2457168        | ARM64_ERRATUM_2457168       |
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Cortex-A510     | #2064142        | ARM64_ERRATUM_2064142       |

arch/arm64/Kconfig

@@ -384,25 +384,6 @@ menu "Kernel Features"
 
 menu "ARM errata workarounds via the alternatives framework"
 
-config AMPERE_ERRATUM_AC03_CPU_38
-        bool "AmpereOne: AC03_CPU_38: Certain bits in the Virtualization Translation Control Register and Translation Control Registers do not follow RES0 semantics"
-	default y
-	help
-	  This option adds an alternative code sequence to work around Ampere
-	  erratum AC03_CPU_38 on AmpereOne.
-
-	  The affected design reports FEAT_HAFDBS as not implemented in
-	  ID_AA64MMFR1_EL1.HAFDBS, but (V)TCR_ELx.{HA,HD} are not RES0
-	  as required by the architecture. The unadvertised HAFDBS
-	  implementation suffers from an additional erratum where hardware
-	  A/D updates can occur after a PTE has been marked invalid.
-
-	  The workaround forces KVM to explicitly set VTCR_EL2.HA to 0,
-	  which avoids enabling unadvertised hardware Access Flag management
-	  at stage-2.
-
-	  If unsure, say Y.
-
 config ARM64_WORKAROUND_CLEAN_CACHE
 	bool
 

arch/arm64/kernel/cpu_errata.c

@@ -722,13 +722,6 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		MIDR_FIXED(MIDR_CPU_VAR_REV(1,1), BIT(25)),
 		.cpu_enable = cpu_clear_bf16_from_user_emulation,
 	},
-#endif
-#ifdef CONFIG_AMPERE_ERRATUM_AC03_CPU_38
-	{
-		.desc = "AmpereOne erratum AC03_CPU_38",
-		.capability = ARM64_WORKAROUND_AMPERE_AC03_CPU_38,
-		ERRATA_MIDR_ALL_VERSIONS(MIDR_AMPERE1),
-	},
 #endif
 	{
 	}

arch/arm64/kvm/hyp/pgtable.c

@@ -543,17 +543,9 @@ u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift)
 #ifdef CONFIG_ARM64_HW_AFDBM
 	/*
 	 * Enable the Hardware Access Flag management, unconditionally
-	 * on all CPUs. In systems that have asymmetric support for the feature
+	 * on all CPUs. The features is RES0 on CPUs without the support
-	 * this allows KVM to leverage hardware support on the subset of cores
+	 * and must be ignored by the CPUs.
-	 * that implement the feature.
-	 *
-	 * The architecture requires VTCR_EL2.HA to be RES0 (thus ignored by
-	 * hardware) on implementations that do not advertise support for the
-	 * feature. As such, setting HA unconditionally is safe, unless you
-	 * happen to be running on a design that has unadvertised support for
-	 * HAFDBS. Here be dragons.
 	 */
-	if (!cpus_have_final_cap(ARM64_WORKAROUND_AMPERE_AC03_CPU_38))
 	vtcr |= VTCR_EL2_HA;
 #endif /* CONFIG_ARM64_HW_AFDBM */
 

arch/arm64/tools/cpucaps

@@ -71,7 +71,6 @@ WORKAROUND_2064142
 WORKAROUND_2077057
 WORKAROUND_2457168
 WORKAROUND_2658417
-WORKAROUND_AMPERE_AC03_CPU_38
 WORKAROUND_TRBE_OVERWRITE_FILL_MODE
 WORKAROUND_TSB_FLUSH_FAILURE
 WORKAROUND_TRBE_WRITE_OUT_OF_RANGE