[PATCH 1/2] arm64: errata: Work around AmpereOne's erratum AC03_CPU_36

D Scott Phillips
2025-04-15T15:47:17Z

AC03_CPU_36 can cause asynchronous exceptions to be routed to the wrong
exception level if an async exception coincides with an update to the
controls for the target exception level in HCR_EL2. On affected
machines, always do writes to HCR_EL2 with async exceptions blocked.

Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com>
---
arch/arm64/Kconfig | 17 +++++++++++++++++
arch/arm64/include/asm/sysreg.h | 18 ++++++++++++++++--
arch/arm64/kernel/cpu_errata.c | 14 ++++++++++++++
arch/arm64/tools/cpucaps | 1 +
4 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a182295e6f08b..e5fd87446a3b8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -445,6 +445,23 @@ menu "Kernel Features"

menu "ARM errata workarounds via the alternatives framework"

+config AMPERE_ERRATUM_AC03_CPU_36
+ bool "AmpereOne: AC03_CPU_36: CPU can take an invalid exception, if an asynchronous exception to EL2 occurs while EL2 software is changing the EL2 exception controls."
+ default y
+ help
+ This option adds an alternative code sequence to work around Ampere
+ errata AC03_CPU_36 on AmpereOne.
+
+ If an async exception happens at the same time as an update to the
+ controls for the target EL for async exceptions, an exception can be
+ delivered to the wrong EL. For example, an EL may be routed from EL2
+ to EL1.
+
+ The workaround masks all asynchronous exception types when writing
+ to HCR_EL2.
+
+ If unsure, say Y.
+
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
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 2639d3633073d..e7781f7e7f7a7 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -1136,14 +1136,28 @@
__val; \
})

+#define __sysreg_is_hcr_el2(r) \
+ (__builtin_strcmp("hcr_el2", __stringify(r)) == 0)
+#define __hcr_el2_ac03_cpu_36(r) \
+ (IS_ENABLED(CONFIG_AMPERE_ERRATUM_AC03_CPU_36) && \
+ __sysreg_is_hcr_el2(r) && \
+ alternative_has_cap_unlikely(ARM64_WORKAROUND_AMPERE_AC03_CPU_36))
+
/*
* The "Z" constraint normally means a zero immediate, but when combined with
* the "%x0" template means XZR.
*/
#define write_sysreg(v, r) do { \
u64 __val = (u64)(v); \
- asm volatile("msr " __stringify(r) ", %x0" \
- : : "rZ" (__val)); \
+ if (__hcr_el2_ac03_cpu_36(r)) { \
+ u64 __daif; \
+ asm volatile("mrs %0, daif; msr daifset, #0xf;" \
+ "msr hcr_el2, %x1; msr daif, %0" \
+ : "=&r"(__daif) : "rZ" (__val)); \
+ } else { \
+ asm volatile("msr " __stringify(r) ", %x0" \
+ : : "rZ" (__val)); \
+ } \
} while (0)

/*
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index b55f5f7057502..89be85bf631fd 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -549,6 +549,13 @@ static const struct midr_range erratum_spec_ssbs_list[] = {
};
#endif

+#ifdef CONFIG_AMPERE_ERRATUM_AC03_CPU_36
+static const struct midr_range erratum_ac03_cpu_36_list[] = {
+ MIDR_ALL_VERSIONS(MIDR_AMPERE1),
+ {},
+};
+#endif
+
#ifdef CONFIG_AMPERE_ERRATUM_AC03_CPU_38
static const struct midr_range erratum_ac03_cpu_38_list[] = {
MIDR_ALL_VERSIONS(MIDR_AMPERE1),
@@ -869,6 +876,13 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
ERRATA_MIDR_RANGE_LIST(erratum_spec_unpriv_load_list),
},
#endif
+#ifdef CONFIG_AMPERE_ERRATUM_AC03_CPU_36
+ {
+ .desc = "AmpereOne erratum AC03_CPU_36",
+ .capability = ARM64_WORKAROUND_AMPERE_AC03_CPU_36,
+ ERRATA_MIDR_RANGE_LIST(erratum_ac03_cpu_36_list),
+ },
+#endif
#ifdef CONFIG_AMPERE_ERRATUM_AC03_CPU_38
{
.desc = "AmpereOne erratum AC03_CPU_38",
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 772c1b008e437..f430fd5900d15 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -93,6 +93,7 @@ WORKAROUND_2077057
WORKAROUND_2457168
WORKAROUND_2645198
WORKAROUND_2658417
+WORKAROUND_AMPERE_AC03_CPU_36
WORKAROUND_AMPERE_AC03_CPU_38
WORKAROUND_TRBE_OVERWRITE_FILL_MODE
WORKAROUND_TSB_FLUSH_FAILURE
--
2.48.1