[PATCH V3] LoongArch: Add unaligned access support

Huacai Chen
2022-10-17T12:53:55Z

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 <chenhuacai@loongson.cn>
---
V2: Simplify READ_FPR and WRITE_FPR.
V3: Cleanup unnecessary code and update documents.

Documentation/admin-guide/sysctl/kernel.rst | 8 +-
arch/loongarch/Kconfig | 2 +
arch/loongarch/include/asm/inst.h | 14 +
arch/loongarch/kernel/Makefile | 3 +-
arch/loongarch/kernel/traps.c | 27 ++
arch/loongarch/kernel/unaligned.c | 390 ++++++++++++++++++++
arch/loongarch/lib/Makefile | 2 +-
arch/loongarch/lib/unaligned.S | 91 +++++
8 files changed, 531 insertions(+), 6 deletions(-)
create mode 100644 arch/loongarch/kernel/unaligned.c
create mode 100644 arch/loongarch/lib/unaligned.S

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 98d1b198b2b4..f2b802cd6208 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/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.
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 0a6ef613124c..a8dc58e8162a 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -122,6 +122,8 @@ 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
diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
index fce1843ceebb..e96b5345f389 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/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;
+
+unsigned long unaligned_read(void *addr, void *value, unsigned long n, bool sign);
+unsigned long unaligned_write(void *addr, unsigned long value, unsigned long n);
+void emulate_load_store_insn(struct pt_regs *regs, void __user *addr, unsigned int *pc);
+
#endif /* _ASM_INST_H */
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 42be564278fa..2ad2555b53ea 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/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
diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
index 1a4dce84ebc6..7ea62faeeadb 100644
--- a/arch/loongarch/kernel/traps.c
+++ b/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);
}

diff --git a/arch/loongarch/kernel/unaligned.c b/arch/loongarch/kernel/unaligned.c
new file mode 100644
index 000000000000..44117cb8ad20
--- /dev/null
+++ b/arch/loongarch/kernel/unaligned.c
@@ -0,0 +1,390 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Handle unaligned accesses by emulation.
+ *
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ *
+ * Derived from MIPS:
+ * Copyright (C) 1996, 1998, 1999, 2002 by Ralf Baechle
+ * Copyright (C) 1999 Silicon Graphics, Inc.
+ * Copyright (C) 2014 Imagination Technologies Ltd.
+ */
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/signal.h>
+#include <linux/debugfs.h>
+#include <linux/perf_event.h>
+
+#include <asm/asm.h>
+#include <asm/branch.h>
+#include <asm/fpu.h>
+#include <asm/inst.h>
+
+#include "access-helper.h"
+
+#ifdef CONFIG_DEBUG_FS
+static u32 unaligned_instructions_user;
+static u32 unaligned_instructions_kernel;
+#endif
+
+static inline unsigned long read_fpr(unsigned int idx)
+{
+#define READ_FPR(idx, __value) \
+ __asm__ __volatile__("movfr2gr.d %0, $f"#idx"\n\t" : "=r"(__value));
+
+ unsigned long __value;
+
+ switch (idx) {
+ case 0:
+ READ_FPR(0, __value);
+ break;
+ case 1:
+ READ_FPR(1, __value);
+ break;
+ case 2:
+ READ_FPR(2, __value);
+ break;
+ case 3:
+ READ_FPR(3, __value);
+ break;
+ case 4:
+ READ_FPR(4, __value);
+ break;
+ case 5:
+ READ_FPR(5, __value);
+ break;
+ case 6:
+ READ_FPR(6, __value);
+ break;
+ case 7:
+ READ_FPR(7, __value);
+ break;
+ case 8:
+ READ_FPR(8, __value);
+ break;
+ case 9:
+ READ_FPR(9, __value);
+ break;
+ case 10:
+ READ_FPR(10, __value);
+ break;
+ case 11:
+ READ_FPR(11, __value);
+ break;
+ case 12:
+ READ_FPR(12, __value);
+ break;
+ case 13:
+ READ_FPR(13, __value);
+ break;
+ case 14:
+ READ_FPR(14, __value);
+ break;
+ case 15:
+ READ_FPR(15, __value);
+ break;
+ case 16:
+ READ_FPR(16, __value);
+ break;
+ case 17:
+ READ_FPR(17, __value);
+ break;
+ case 18:
+ READ_FPR(18, __value);
+ break;
+ case 19:
+ READ_FPR(19, __value);
+ break;
+ case 20:
+ READ_FPR(20, __value);
+ break;
+ case 21:
+ READ_FPR(21, __value);
+ break;
+ case 22:
+ READ_FPR(22, __value);
+ break;
+ case 23:
+ READ_FPR(23, __value);
+ break;
+ case 24:
+ READ_FPR(24, __value);
+ break;
+ case 25:
+ READ_FPR(25, __value);
+ break;
+ case 26:
+ READ_FPR(26, __value);
+ break;
+ case 27:
+ READ_FPR(27, __value);
+ break;
+ case 28:
+ READ_FPR(28, __value);
+ break;
+ case 29:
+ READ_FPR(29, __value);
+ break;
+ case 30:
+ READ_FPR(30, __value);
+ break;
+ case 31:
+ READ_FPR(31, __value);
+ break;
+ default:
+ panic("unexpected idx '%d'", idx);
+ }
+#undef READ_FPR
+ return __value;
+}
+
+static inline void write_fpr(unsigned int idx, unsigned long value)
+{
+#define WRITE_FPR(idx, value) \
+ __asm__ __volatile__("movgr2fr.d $f"#idx", %0\n\t" :: "r"(value));
+
+ switch (idx) {
+ case 0:
+ WRITE_FPR(0, value);
+ break;
+ case 1:
+ WRITE_FPR(1, value);
+ break;
+ case 2:
+ WRITE_FPR(2, value);
+ break;
+ case 3:
+ WRITE_FPR(3, value);
+ break;
+ case 4:
+ WRITE_FPR(4, value);
+ break;
+ case 5:
+ WRITE_FPR(5, value);
+ break;
+ case 6:
+ WRITE_FPR(6, value);
+ break;
+ case 7:
+ WRITE_FPR(7, value);
+ break;
+ case 8:
+ WRITE_FPR(8, value);
+ break;
+ case 9:
+ WRITE_FPR(9, value);
+ break;
+ case 10:
+ WRITE_FPR(10, value);
+ break;
+ case 11:
+ WRITE_FPR(11, value);
+ break;
+ case 12:
+ WRITE_FPR(12, value);
+ break;
+ case 13:
+ WRITE_FPR(13, value);
+ break;
+ case 14:
+ WRITE_FPR(14, value);
+ break;
+ case 15:
+ WRITE_FPR(15, value);
+ break;
+ case 16:
+ WRITE_FPR(16, value);
+ break;
+ case 17:
+ WRITE_FPR(17, value);
+ break;
+ case 18:
+ WRITE_FPR(18, value);
+ break;
+ case 19:
+ WRITE_FPR(19, value);
+ break;
+ case 20:
+ WRITE_FPR(20, value);
+ break;
+ case 21:
+ WRITE_FPR(21, value);
+ break;
+ case 22:
+ WRITE_FPR(22, value);
+ break;
+ case 23:
+ WRITE_FPR(23, value);
+ break;
+ case 24:
+ WRITE_FPR(24, value);
+ break;
+ case 25:
+ WRITE_FPR(25, value);
+ break;
+ case 26:
+ WRITE_FPR(26, value);
+ break;
+ case 27:
+ WRITE_FPR(27, value);
+ break;
+ case 28:
+ WRITE_FPR(28, value);
+ break;
+ case 29:
+ WRITE_FPR(29, value);
+ break;
+ case 30:
+ WRITE_FPR(30, value);
+ break;
+ case 31:
+ WRITE_FPR(31, value);
+ break;
+ default:
+ panic("unexpected idx '%d'", idx);
+ }
+#undef WRITE_FPR
+}
+
+void emulate_load_store_insn(struct pt_regs *regs, void __user *addr, unsigned int *pc)
+{
+ bool user = user_mode(regs);
+ unsigned int res;
+ unsigned long value = 0;
+ union loongarch_instruction insn;
+
+ perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, 0);
+
+ /*
+ * This load never faults.
+ */
+ __get_inst(&insn.word, pc, user);
+ if (user && !access_ok(addr, 8))
+ goto sigbus;
+
+ if (insn.reg2i12_format.opcode == ldd_op ||
+ insn.reg2i14_format.opcode == ldptrd_op ||
+ insn.reg3_format.opcode == ldxd_op) {
+ res = unaligned_read(addr, &value, 8, 1);
+ if (res)
+ goto fault;
+ regs->regs[insn.reg2i12_format.rd] = value;
+ } else if (insn.reg2i12_format.opcode == ldw_op ||
+ insn.reg2i14_format.opcode == ldptrw_op ||
+ insn.reg3_format.opcode == ldxw_op) {
+ res = unaligned_read(addr, &value, 4, 1);
+ if (res)
+ goto fault;
+ regs->regs[insn.reg2i12_format.rd] = value;
+ } else if (insn.reg2i12_format.opcode == ldwu_op ||
+ insn.reg3_format.opcode == ldxwu_op) {
+ res = unaligned_read(addr, &value, 4, 0);
+ if (res)
+ goto fault;
+ regs->regs[insn.reg2i12_format.rd] = value;
+ } else if (insn.reg2i12_format.opcode == ldh_op ||
+ insn.reg3_format.opcode == ldxh_op) {
+ res = unaligned_read(addr, &value, 2, 1);
+ if (res)
+ goto fault;
+ regs->regs[insn.reg2i12_format.rd] = value;
+ } else if (insn.reg2i12_format.opcode == ldhu_op ||
+ insn.reg3_format.opcode == ldxhu_op) {
+ res = unaligned_read(addr, &value, 2, 0);
+ if (res)
+ goto fault;
+ regs->regs[insn.reg2i12_format.rd] = value;
+ } else if (insn.reg2i12_format.opcode == std_op ||
+ insn.reg2i14_format.opcode == stptrd_op ||
+ insn.reg3_format.opcode == stxd_op) {
+ value = regs->regs[insn.reg2i12_format.rd];
+ res = unaligned_write(addr, value, 8);
+ if (res)
+ goto fault;
+ } else if (insn.reg2i12_format.opcode == stw_op ||
+ insn.reg2i14_format.opcode == stptrw_op ||
+ insn.reg3_format.opcode == stxw_op) {
+ value = regs->regs[insn.reg2i12_format.rd];
+ res = unaligned_write(addr, value, 4);
+ if (res)
+ goto fault;
+ } else if (insn.reg2i12_format.opcode == sth_op ||
+ insn.reg3_format.opcode == stxh_op) {
+ value = regs->regs[insn.reg2i12_format.rd];
+ res = unaligned_write(addr, value, 2);
+ if (res)
+ goto fault;
+ } else if (insn.reg2i12_format.opcode == fldd_op ||
+ insn.reg3_format.opcode == fldxd_op) {
+ res = unaligned_read(addr, &value, 8, 1);
+ if (res)
+ goto fault;
+ write_fpr(insn.reg2i12_format.rd, value);
+ } else if (insn.reg2i12_format.opcode == flds_op ||
+ insn.reg3_format.opcode == fldxs_op) {
+ res = unaligned_read(addr, &value, 4, 1);
+ if (res)
+ goto fault;
+ write_fpr(insn.reg2i12_format.rd, value);
+ } else if (insn.reg2i12_format.opcode == fstd_op ||
+ insn.reg3_format.opcode == fstxd_op) {
+ value = read_fpr(insn.reg2i12_format.rd);
+ res = unaligned_write(addr, value, 8);
+ if (res)
+ goto fault;
+ } else if (insn.reg2i12_format.opcode == fsts_op ||
+ insn.reg3_format.opcode == fstxs_op) {
+ value = read_fpr(insn.reg2i12_format.rd);
+ res = unaligned_write(addr, value, 4);
+ if (res)
+ goto fault;
+ } else
+ goto sigbus;
+
+
+#ifdef CONFIG_DEBUG_FS
+ if (user)
+ unaligned_instructions_user++;
+ else
+ unaligned_instructions_kernel++;
+#endif
+
+ compute_return_era(regs);
+
+ return;
+
+fault:
+ /* Did we have an exception handler installed? */
+ if (fixup_exception(regs))
+ return;
+
+ die_if_kernel("Unhandled kernel unaligned access", regs);
+ force_sig(SIGSEGV);
+
+ return;
+
+sigbus:
+ die_if_kernel("Unhandled kernel unaligned access", regs);
+ force_sig(SIGBUS);
+
+ return;
+}
+
+#ifdef CONFIG_DEBUG_FS
+static int __init debugfs_unaligned(void)
+{
+ struct dentry *d;
+
+ d = debugfs_create_dir("loongarch", NULL);
+ if (!d)
+ return -ENOMEM;
+
+ debugfs_create_u32("unaligned_instructions_user",
+ S_IRUGO, d, &unaligned_instructions_user);
+ debugfs_create_u32("unaligned_instructions_kernel",
+ S_IRUGO, d, &unaligned_instructions_kernel);
+
+ return 0;
+}
+arch_initcall(debugfs_unaligned);
+#endif
diff --git a/arch/loongarch/lib/Makefile b/arch/loongarch/lib/Makefile
index e36635fccb69..867895530340 100644
--- a/arch/loongarch/lib/Makefile
+++ b/arch/loongarch/lib/Makefile
@@ -3,4 +3,4 @@
# Makefile for LoongArch-specific library files.
#

-lib-y += delay.o clear_user.o copy_user.o dump_tlb.o
+lib-y += delay.o clear_user.o copy_user.o dump_tlb.o unaligned.o
diff --git a/arch/loongarch/lib/unaligned.S b/arch/loongarch/lib/unaligned.S
new file mode 100644
index 000000000000..b42c4a2edfad
--- /dev/null
+++ b/arch/loongarch/lib/unaligned.S
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/asm.h>
+#include <asm/asmmacro.h>
+#include <asm/errno.h>
+#include <asm/export.h>
+#include <asm/regdef.h>
+
+.macro fixup_ex from, to, fix
+.if \fix
+ .section .fixup, "ax"
+\to: li.w a0, -EFAULT
+ jr ra
+ .previous
+.endif
+ .section __ex_table, "a"
+ PTR \from\()b, \to\()b
+ .previous
+.endm
+
+/*
+ * unsigned long unaligned_read(void *addr, void *value, unsigned long n, bool sign)
+ *
+ * a0: addr
+ * a1: value
+ * a2: n
+ * a3: sign
+ */
+SYM_FUNC_START(unaligned_read)
+ beqz a2, 5f
+
+ li.w t2, 0
+ addi.d t0, a2, -1
+ slli.d t1, t0, 3
+ add.d a0, a0, t0
+
+ beqz a3, 2f
+1: ld.b t3, a0, 0
+ b 3f
+
+2: ld.bu t3, a0, 0
+3: sll.d t3, t3, t1
+ or t2, t2, t3
+ addi.d t1, t1, -8
+ addi.d a0, a0, -1
+ addi.d a2, a2, -1
+ bgtz a2, 2b
+4: st.d t2, a1, 0
+
+ move a0, a2
+ jr ra
+
+5: li.w a0, -EFAULT
+ jr ra
+
+ fixup_ex 1, 6, 1
+ fixup_ex 2, 6, 0
+ fixup_ex 4, 6, 0
+SYM_FUNC_END(unaligned_read)
+
+/*
+ * unsigned long unaligned_write(void *addr, unsigned long value, unsigned long n)
+ *
+ * a0: addr
+ * a1: value
+ * a2: n
+ */
+SYM_FUNC_START(unaligned_write)
+ beqz a2, 3f
+
+ li.w t0, 0
+1: srl.d t1, a1, t0
+2: st.b t1, a0, 0
+ addi.d t0, t0, 8
+ addi.d a2, a2, -1
+ addi.d a0, a0, 1
+ bgtz a2, 1b
+
+ move a0, a2
+ jr ra
+
+3: li.w a0, -EFAULT
+ jr ra
+
+ fixup_ex 2, 4, 1
+SYM_FUNC_END(unaligned_write)
--
2.31.1