linux-kernel - [PATCH v2 1/4] arm64: Introduce aarch32

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Date:   Mon, 23 Oct 2023 16:42:20 +0200
From:   Andrea della Porta <andrea.porta@...e.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     nik.borisov@...e.com, arnd@...db.de, mark.rutland@....com,
        Andrea della Porta <andrea.porta@...e.com>
Subject: [PATCH v2 1/4] arm64: Introduce aarch32_enabled()

Aarch32 bit support on 64bit kernels depends on whether CONFIG_COMPAT
is selected or not. As it is a compile time option it doesn't
provide the flexibility to have distributions set their own policy for
Aarch32 support and give the user the flexibility to override it.

As a first step introduce aarch32_enabled() which abstracts whether 32
bit compat is turned on or off. Upcoming patches will implement
the ability to set Aarch32 compat state at boot time.

Signed-off-by: Andrea della Porta <andrea.porta@...e.com>
---
 arch/arm64/include/asm/cpufeature.h | 15 +++++++++++++++
 arch/arm64/kernel/entry-common.c    |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 396af9b9c857..1180d68daaff 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -657,6 +657,21 @@ static inline bool supports_clearbhb(int scope)
 						    ID_AA64ISAR2_EL1_CLRBHB_SHIFT);
 }
 
+#ifdef CONFIG_COMPAT
+extern bool __aarch32_enabled;
+
+static inline bool aarch32_enabled(void)
+{
+	return __aarch32_enabled;
+}
+#else /* !CONFIG_COMPAT */
+
+static inline bool aarch32_enabled(void)
+{
+	return false;
+}
+#endif
+
 const struct cpumask *system_32bit_el0_cpumask(void);
 DECLARE_STATIC_KEY_FALSE(arm64_mismatched_32bit_el0);
 
diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 0fc94207e69a..69ff9b8c0bde 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -877,6 +877,8 @@ asmlinkage void noinstr el0t_32_error_handler(struct pt_regs *regs)
 {
 	__el0_error_handler_common(regs);
 }
+
+bool __aarch32_enabled __ro_after_init = true;
 #else /* CONFIG_COMPAT */
 UNHANDLED(el0t, 32, sync)
 UNHANDLED(el0t, 32, irq)
-- 
2.35.3