Re: [PATCH V2] LoongArch: Add unaligned access support

From: Huacai Chen
Date: Mon Oct 17 2022 - 03:41:09 EST

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In reply to: WANG Xuerui: "Re: [PATCH V2] LoongArch: Add unaligned access support"
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Hi, Xuerui,

On Mon, Oct 17, 2022 at 2:07 PM WANG Xuerui <kernel@xxxxxxxxxx> wrote:
>
> On 2022/10/17 10:23, Huacai Chen wrote:
> > 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@xxxxxxxxxxx>
> > ---
> > V2: Simplify READ_FPR and WRITE_FPR.
> >
> > 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 | 393 ++++++++++++++++++++++++++++++
> > arch/loongarch/lib/Makefile | 2 +-
> > arch/loongarch/lib/unaligned.S | 93 +++++++
> > 7 files changed, 532 insertions(+), 2 deletions(-)
> > create mode 100644 arch/loongarch/kernel/unaligned.c
> > create mode 100644 arch/loongarch/lib/unaligned.S
>
> Please also update Documentation/admin-guide/sysctl/kernel.rst to
> mention loongarch in the respective sysctls' documentation. (Grep for
> ARCH_UNALIGN to see.)
OK, thanks.

>
> >
> > 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..f367424b762a
> > --- /dev/null
> > +++ b/arch/loongarch/kernel/unaligned.c
> > @@ -0,0 +1,393 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Handle unaligned accesses by emulation.
> > + *
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
>
> MIPS heritage too?
>
> > + *
> > + */
> > +#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 fd)
> > +{
> > +#define READ_FPR(fd, __value) \
> > + __asm__ __volatile__("movfr2gr.d %0, $f"#fd"\n\t" : "=r"(__value));
> > +
> > + unsigned long __value;
> > +
> > + switch (fd) {
> > + 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 fd '%d'", fd);
>
> So this is a bit misleading, I was thinking of file descriptors when I
> was reading Feiyang's review comments... maybe something as simple as
> "idx", "num" or "regno" will do?
OK, idx is better.

>
> > + }
> > +#undef READ_FPR
> > + return __value;
> > +}
> > +
> > +static inline void write_fpr(unsigned int fd, unsigned long value)
> > +{
> > +#define WRITE_FPR(fd, value) \
> > + __asm__ __volatile__("movgr2fr.d $f"#fd", %0\n\t" :: "r"(value));
> > +
> > + switch (fd) {
> > + 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 fd '%d'", fd);
> > + }
> > +#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 origpc;
> > + unsigned long origra;
> > + unsigned long value = 0;
> > + union loongarch_instruction insn;
> > +
> > + origpc = (unsigned long)pc;
> > + origra = regs->regs[1];
> > +
> > + 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:
> > + /* roll back jump/branch */
> > + regs->csr_era = origpc;
> > + regs->regs[1] = origra;
> > + /* 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..03210cb5a18d
> > --- /dev/null
> > +++ b/arch/loongarch/lib/unaligned.S
> > @@ -0,0 +1,93 @@
> > +/* 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 t1, 8
> > + li.w t2, 0
> > +
> > + addi.d t0, a2, -1
> > + mul.d t1, t0, t1
>
> Remove the `t1 = 8` above, then `slli.d t1, t0, 3` here would be enough
> and one cycle is saved.
OK, thanks.

Huacai
>
> > + add.d a0, a0, t0
> > +
> > + beq a3, zero, 2f
>
> beqz
>
> > +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
> > + bgt a2, zero, 2b
>
> bgtz
>
> > +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
> > + bgt a2, zero, 1b
>
> bgtz
>
> > +
> > + move a0, a2
> > + jr ra
> > +
> > +3: li.w a0, -EFAULT
> > + jr ra
> > +
> > + fixup_ex 2, 4, 1
> > +SYM_FUNC_END(unaligned_write)
>
> --
> WANG "xen0n" Xuerui
>
> Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/
>
>

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