[PATCH v12 7/7] arm64: armv8_deprecated: disable swp emulation when FEAT_LSUI present
From: Yeoreum Yun <hidden>
Date: 2026-01-21 19:06:52
Also in:
kvm, kvmarm, linux-kselftest, lkml
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
The purpose of supporting LSUI is to eliminate PAN toggling. CPUs that support LSUI are unlikely to support a 32-bit runtime. Since environments that support both LSUI and a 32-bit runtimeare expected to be extremely rare, not to emulate the SWP instruction using LSUI instructions in order to remove PAN toggling, and instead simply disable SWP emulation. Signed-off-by: Yeoreum Yun <redacted> --- arch/arm64/kernel/armv8_deprecated.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
index e737c6295ec7..049754f7da36 100644
--- a/arch/arm64/kernel/armv8_deprecated.c
+++ b/arch/arm64/kernel/armv8_deprecated.c@@ -610,6 +610,22 @@ static int __init armv8_deprecated_init(void) } #endif + +#ifdef CONFIG_SWP_EMULATION + /* + * The purpose of supporting LSUI is to eliminate PAN toggling. + * CPUs that support LSUI are unlikely to support a 32-bit runtime. + * Since environments that support both LSUI and a 32-bit runtime + * are expected to be extremely rare, we choose not to emulate + * the SWP instruction using LSUI instructions in order to remove PAN toggling, + * and instead simply disable SWP emulation. + */ + if (cpus_have_final_cap(ARM64_HAS_LSUI)) { + insn_swp.status = INSN_UNAVAILABLE; + pr_info("swp/swpb instruction emulation is not supported on this system\n"); + } +#endif + for (int i = 0; i < ARRAY_SIZE(insn_emulations); i++) { struct insn_emulation *ie = insn_emulations[i];
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