arm64: entry: convert el1_sync to C

This patch converts the EL1 sync entry assembly logic to C code.

Doing this will allow us to make changes in a slightly more
readable way. A case in point is supporting kernel-first RAS.
do_sea() should be called on the CPU that took the fault.

Largely the assembly code is converted to C in a relatively
straightforward manner.

Since all sync sites share a common asm entry point, the ASM_BUG()
instances are no longer required for effective backtraces back to
assembly, and we don't need similar BUG() entries.

The ESR_ELx.EC codes for all (supported) debug exceptions are now
checked in the el1_sync_handler's switch statement, which renders the
check in el1_dbg redundant. This both simplifies the el1_dbg handler,
and makes the EL1 exception handling more robust to
currently-unallocated ESR_ELx.EC encodings.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
[split out of a bigger series, added nokprobes, moved prototypes]
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/Makefile

@@ -13,9 +13,9 @@ CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
 
 # Object file lists.
 obj-y			:= debug-monitors.o entry.o irq.o fpsimd.o		\
-			   entry-fpsimd.o process.o ptrace.o setup.o signal.o	\
-			   sys.o stacktrace.o time.o traps.o io.o vdso.o	\
-			   hyp-stub.o psci.o cpu_ops.o insn.o	\
+			   entry-common.o entry-fpsimd.o process.o ptrace.o	\
+			   setup.o signal.o sys.o stacktrace.o time.o traps.o	\
+			   io.o vdso.o hyp-stub.o psci.o cpu_ops.o insn.o	\
 			   return_address.o cpuinfo.o cpu_errata.o		\
 			   cpufeature.o alternative.o cacheinfo.o		\
 			   smp.o smp_spin_table.o topology.o smccc-call.o	\

arch/arm64/kernel/entry-common.c

@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Exception handling code
+ *
+ * Copyright (C) 2019 ARM Ltd.
+ */
+
+#include <linux/context_tracking.h>
+#include <linux/ptrace.h>
+#include <linux/thread_info.h>
+
+#include <asm/cpufeature.h>
+#include <asm/daifflags.h>
+#include <asm/esr.h>
+#include <asm/exception.h>
+#include <asm/kprobes.h>
+#include <asm/sysreg.h>
+
+static void notrace el1_abort(struct pt_regs *regs, unsigned long esr)
+{
+	unsigned long far = read_sysreg(far_el1);
+
+	local_daif_inherit(regs);
+	far = untagged_addr(far);
+	do_mem_abort(far, esr, regs);
+}
+NOKPROBE_SYMBOL(el1_abort);
+
+static void notrace el1_pc(struct pt_regs *regs, unsigned long esr)
+{
+	unsigned long far = read_sysreg(far_el1);
+
+	local_daif_inherit(regs);
+	do_sp_pc_abort(far, esr, regs);
+}
+NOKPROBE_SYMBOL(el1_pc);
+
+static void el1_undef(struct pt_regs *regs)
+{
+	local_daif_inherit(regs);
+	do_undefinstr(regs);
+}
+NOKPROBE_SYMBOL(el1_undef);
+
+static void el1_inv(struct pt_regs *regs, unsigned long esr)
+{
+	local_daif_inherit(regs);
+	bad_mode(regs, 0, esr);
+}
+NOKPROBE_SYMBOL(el1_inv);
+
+static void notrace el1_dbg(struct pt_regs *regs, unsigned long esr)
+{
+	unsigned long far = read_sysreg(far_el1);
+
+	/*
+	 * The CPU masked interrupts, and we are leaving them masked during
+	 * do_debug_exception(). Update PMR as if we had called
+	 * local_mask_daif().
+	 */
+	if (system_uses_irq_prio_masking())
+		gic_write_pmr(GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET);
+
+	do_debug_exception(far, esr, regs);
+}
+NOKPROBE_SYMBOL(el1_dbg);
+
+asmlinkage void notrace el1_sync_handler(struct pt_regs *regs)
+{
+	unsigned long esr = read_sysreg(esr_el1);
+
+	switch (ESR_ELx_EC(esr)) {
+	case ESR_ELx_EC_DABT_CUR:
+	case ESR_ELx_EC_IABT_CUR:
+		el1_abort(regs, esr);
+		break;
+	/*
+	 * We don't handle ESR_ELx_EC_SP_ALIGN, since we will have hit a
+	 * recursive exception when trying to push the initial pt_regs.
+	 */
+	case ESR_ELx_EC_PC_ALIGN:
+		el1_pc(regs, esr);
+		break;
+	case ESR_ELx_EC_SYS64:
+	case ESR_ELx_EC_UNKNOWN:
+		el1_undef(regs);
+		break;
+	case ESR_ELx_EC_BREAKPT_CUR:
+	case ESR_ELx_EC_SOFTSTP_CUR:
+	case ESR_ELx_EC_WATCHPT_CUR:
+	case ESR_ELx_EC_BRK64:
+		el1_dbg(regs, esr);
+		break;
+	default:
+		el1_inv(regs, esr);
+	};
+}
+NOKPROBE_SYMBOL(el1_sync_handler);

arch/arm64/kernel/entry.S

@@ -578,76 +578,9 @@ ENDPROC(el1_error_invalid)
 	.align	6
 el1_sync:
 	kernel_entry 1
-	mrs	x1, esr_el1			// read the syndrome register
-	lsr	x24, x1, #ESR_ELx_EC_SHIFT	// exception class
-	cmp	x24, #ESR_ELx_EC_DABT_CUR	// data abort in EL1
-	b.eq	el1_da
-	cmp	x24, #ESR_ELx_EC_IABT_CUR	// instruction abort in EL1
-	b.eq	el1_ia
-	cmp	x24, #ESR_ELx_EC_SYS64		// configurable trap
-	b.eq	el1_undef
-	cmp	x24, #ESR_ELx_EC_PC_ALIGN	// pc alignment exception
-	b.eq	el1_pc
-	cmp	x24, #ESR_ELx_EC_UNKNOWN	// unknown exception in EL1
-	b.eq	el1_undef
-	cmp	x24, #ESR_ELx_EC_BREAKPT_CUR	// debug exception in EL1
-	b.ge	el1_dbg
-	b	el1_inv
-
-el1_ia:
-	/*
-	 * Fall through to the Data abort case
-	 */
-el1_da:
-	/*
-	 * Data abort handling
-	 */
-	mrs	x3, far_el1
-	inherit_daif	pstate=x23, tmp=x2
-	clear_address_tag x0, x3
-	mov	x2, sp				// struct pt_regs
-	bl	do_mem_abort
-
-	kernel_exit 1
-el1_pc:
-	/*
-	 * PC alignment exception handling. We don't handle SP alignment faults,
-	 * since we will have hit a recursive exception when trying to push the
-	 * initial pt_regs.
-	 */
-	mrs	x0, far_el1
-	inherit_daif	pstate=x23, tmp=x2
-	mov	x2, sp
-	bl	do_sp_pc_abort
-	ASM_BUG()
-el1_undef:
-	/*
-	 * Undefined instruction
-	 */
-	inherit_daif	pstate=x23, tmp=x2
 	mov	x0, sp
-	bl	do_undefinstr
+	bl	el1_sync_handler
 	kernel_exit 1
-el1_dbg:
-	/*
-	 * Debug exception handling
-	 */
-	cmp	x24, #ESR_ELx_EC_BRK64		// if BRK64
-	cinc	x24, x24, eq			// set bit '0'
-	tbz	x24, #0, el1_inv		// EL1 only
-	gic_prio_kentry_setup tmp=x3
-	mrs	x0, far_el1
-	mov	x2, sp				// struct pt_regs
-	bl	do_debug_exception
-	kernel_exit 1
-el1_inv:
-	// TODO: add support for undefined instructions in kernel mode
-	inherit_daif	pstate=x23, tmp=x2
-	mov	x0, sp
-	mov	x2, x1
-	mov	x1, #BAD_SYNC
-	bl	bad_mode
-	ASM_BUG()
 ENDPROC(el1_sync)
 
 	.align	6