LoongArch: Add unaligned access support

Loongson-2 series (Loongson-2K500, Loongson-2K1000) don't support
unaligned access in hardware, while Loongson-3 series (Loongson-3A5000,
Loongson-3C5000) are configurable whether support unaligned access in
hardware. This patch add unaligned access emulation for those LoongArch
processors without hardware support.

Signed-off-by: Huacai Chen <[email protected]>

Author: chenhuacai

Documentation/admin-guide/sysctl/kernel.rst

@@ -433,8 +433,8 @@ ignore-unaligned-usertrap
 
 On architectures where unaligned accesses cause traps, and where this
 feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_NO_WARN``;
-currently, ``arc`` and ``ia64``), controls whether all unaligned traps
-are logged.
+currently, ``arc``, ``ia64`` and ``loongarch``), controls whether all
+unaligned traps are logged.
 
 = =============================================================
 0 Log all unaligned accesses.
@@ -1457,8 +1457,8 @@ unaligned-trap
 
 On architectures where unaligned accesses cause traps, and where this
 feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_ALLOW``; currently,
-``arc`` and ``parisc``), controls whether unaligned traps are caught
-and emulated (instead of failing).
+``arc``, ``parisc`` and ``loongarch``), controls whether unaligned traps
+are caught and emulated (instead of failing).
 
 = ========================================================
 0 Do not emulate unaligned accesses.

arch/loongarch/Kconfig

@@ -121,6 +121,8 @@ config LOONGARCH
 	select RTC_LIB
 	select SMP
 	select SPARSE_IRQ
+	select SYSCTL_ARCH_UNALIGN_ALLOW
+	select SYSCTL_ARCH_UNALIGN_NO_WARN
 	select SYSCTL_EXCEPTION_TRACE
 	select SWIOTLB
 	select TRACE_IRQFLAGS_SUPPORT

arch/loongarch/include/asm/inst.h

@@ -76,6 +76,10 @@ enum reg2i12_op {
 	ldbu_op		= 0xa8,
 	ldhu_op		= 0xa9,
 	ldwu_op		= 0xaa,
+	flds_op		= 0xac,
+	fsts_op		= 0xad,
+	fldd_op		= 0xae,
+	fstd_op		= 0xaf,
 };
 
 enum reg2i14_op {
@@ -146,6 +150,10 @@ enum reg3_op {
 	ldxbu_op	= 0x7040,
 	ldxhu_op	= 0x7048,
 	ldxwu_op	= 0x7050,
+	fldxs_op	= 0x7060,
+	fldxd_op	= 0x7068,
+	fstxs_op	= 0x7070,
+	fstxd_op	= 0x7078,
 	amswapw_op	= 0x70c0,
 	amswapd_op	= 0x70c1,
 	amaddw_op	= 0x70c2,
@@ -566,4 +574,10 @@ static inline void emit_##NAME(union loongarch_instruction *insn,	\
 
 DEF_EMIT_REG3SA2_FORMAT(alsld, alsld_op)
 
+struct pt_regs;
+
+void emulate_load_store_insn(struct pt_regs *regs, void __user *addr, unsigned int *pc);
+unsigned long unaligned_read(void __user *addr, void *value, unsigned long n, bool sign);
+unsigned long unaligned_write(void __user *addr, unsigned long value, unsigned long n);
+
 #endif /* _ASM_INST_H */

arch/loongarch/include/asm/thread_info.h

@@ -38,7 +38,7 @@ struct thread_info {
 #define INIT_THREAD_INFO(tsk)			\
 {						\
 	.task		= &tsk,			\
-	.flags		= 0,			\
+	.flags		= _TIF_FIXADE,		\
 	.cpu		= 0,			\
 	.preempt_count	= INIT_PREEMPT_COUNT,	\
 }

arch/loongarch/kernel/Makefile

@@ -7,7 +7,8 @@ extra-y		:= vmlinux.lds
 
 obj-y		+= head.o cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
 		   traps.o irq.o idle.o process.o dma.o mem.o io.o reset.o switch.o \
-		   elf.o syscall.o signal.o time.o topology.o inst.o ptrace.o vdso.o
+		   elf.o syscall.o signal.o time.o topology.o inst.o ptrace.o vdso.o \
+		   unaligned.o
 
 obj-$(CONFIG_ACPI)		+= acpi.o
 obj-$(CONFIG_EFI) 		+= efi.o

arch/loongarch/kernel/traps.c

@@ -368,13 +368,40 @@ asmlinkage void noinstr do_ade(struct pt_regs *regs)
 	irqentry_exit(regs, state);
 }
 
+/* sysctl hooks */
+int unaligned_enabled __read_mostly = 1;	/* Enabled by default */
+int no_unaligned_warning __read_mostly = 1;	/* Only 1 warning by default */
+
 asmlinkage void noinstr do_ale(struct pt_regs *regs)
 {
+	unsigned int *pc;
 	irqentry_state_t state = irqentry_enter(regs);
 
+	perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, regs->csr_badvaddr);
+
+	/*
+	 * Did we catch a fault trying to load an instruction?
+	 */
+	if (regs->csr_badvaddr == regs->csr_era)
+		goto sigbus;
+	if (user_mode(regs) && !test_thread_flag(TIF_FIXADE))
+		goto sigbus;
+	if (!unaligned_enabled)
+		goto sigbus;
+	if (!no_unaligned_warning)
+		show_registers(regs);
+
+	pc = (unsigned int *)exception_era(regs);
+
+	emulate_load_store_insn(regs, (void __user *)regs->csr_badvaddr, pc);
+
+	goto out;
+
+sigbus:
 	die_if_kernel("Kernel ale access", regs);
 	force_sig_fault(SIGBUS, BUS_ADRALN, (void __user *)regs->csr_badvaddr);
 
+out:
 	irqentry_exit(regs, state);
 }