[PATCH RESEND v7 1/6] arm64: cpufeature: add FEAT_LSUI

Yeoreum Yun
2025-08-16T15:19:37Z

Since Armv9.6, FEAT_LSUI supplies load/store instructions
for privileged level to access user memory without clearing PSTATE.PAN bit.

Add LSUI feature so that the unprevilieged load/store instructions
could be used when kernel accesses user memory without clearing PSTATE.PAN bit.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
arch/arm64/kernel/cpufeature.c | 10 ++++++++++
arch/arm64/tools/cpucaps | 1 +
2 files changed, 11 insertions(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9ad065f15f1d..b8660c8d51b2 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -278,6 +278,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar2[] = {

static const struct arm64_ftr_bits ftr_id_aa64isar3[] = {
ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR3_EL1_FPRCVT_SHIFT, 4, 0),
+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR3_EL1_LSUI_SHIFT, 4, ID_AA64ISAR3_EL1_LSUI_NI),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR3_EL1_FAMINMAX_SHIFT, 4, 0),
ARM64_FTR_END,
};
@@ -3131,6 +3132,15 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.matches = has_cpuid_feature,
ARM64_CPUID_FIELDS(ID_AA64PFR2_EL1, GCIE, IMP)
},
+#ifdef CONFIG_AS_HAS_LSUI
+ {
+ .desc = "Unprivileged Load Store Instructions (LSUI)",
+ .capability = ARM64_HAS_LSUI,
+ .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+ .matches = has_cpuid_feature,
+ ARM64_CPUID_FIELDS(ID_AA64ISAR3_EL1, LSUI, IMP)
+ },
+#endif
{},
};

diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index ef0b7946f5a4..73f8e5211cd2 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -44,6 +44,7 @@ HAS_HCX
HAS_LDAPR
HAS_LPA2
HAS_LSE_ATOMICS
+HAS_LSUI
HAS_MOPS
HAS_NESTED_VIRT
HAS_BBML2_NOABORT
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}