Re: [PATCH v2 1/3] LoongArch: Add kexec support

[Huacai Chen]

Hi, Youling,

On Fri, Sep 9, 2022 at 11:20 AM Youling Tang <tangyouling@xxxxxxxxxxx> wrote:
>
> Add three new files, kexec.h, machine_kexec.c and relocate_kernel.S to the
> LoongArch architecture that add support for the kexec re-boot mechanis
> (CONFIG_KEXEC) on LoongArch platforms.
>
> Supports loading vmlinux (vmlinux.elf) in ELF format and vmlinux.efi in
> PE format.
>
> I tested this on  LoongArch 3A5000 machine and works as expected,
>
>  $ sudo kexec -l /boot/vmlinux.efi --reuse-cmdline
>  $ sudo kexec -e
>
> Signed-off-by: Youling Tang <tangyouling@xxxxxxxxxxx>
> ---
>  arch/loongarch/Kconfig                  |  11 ++
>  arch/loongarch/include/asm/kexec.h      |  58 ++++++++
>  arch/loongarch/kernel/Makefile          |   2 +
>  arch/loongarch/kernel/head.S            |   7 +-
>  arch/loongarch/kernel/machine_kexec.c   | 188 ++++++++++++++++++++++++
>  arch/loongarch/kernel/relocate_kernel.S | 106 +++++++++++++
>  6 files changed, 371 insertions(+), 1 deletion(-)
>  create mode 100644 arch/loongarch/include/asm/kexec.h
>  create mode 100644 arch/loongarch/kernel/machine_kexec.c
>  create mode 100644 arch/loongarch/kernel/relocate_kernel.S
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 9b1f2ab878e9..08e063aaf847 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -422,6 +422,17 @@ config ARCH_IOREMAP
>           protection support. However, you can enable LoongArch DMW-based
>           ioremap() for better performance.
>
> +config KEXEC
> +       bool "Kexec system call"
> +       select KEXEC_CORE
> +       help
> +         kexec is a system call that implements the ability to shutdown your
> +         current kernel, and to start another kernel.  It is like a reboot
> +         but it is independent of the system firmware.   And like a reboot
> +         you can start any kernel with it, not just Linux.
> +
> +         The name comes from the similarity to the exec system call.
> +
>  config SECCOMP
>         bool "Enable seccomp to safely compute untrusted bytecode"
>         depends on PROC_FS
> diff --git a/arch/loongarch/include/asm/kexec.h b/arch/loongarch/include/asm/kexec.h
> new file mode 100644
> index 000000000000..f23506725e00
> --- /dev/null
> +++ b/arch/loongarch/include/asm/kexec.h
> @@ -0,0 +1,58 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * kexec.h for kexec
> + *
> + * Copyright (C) 2022 Loongson Technology Corporation Limited
> + */
> +
> +#ifndef _ASM_KEXEC_H
> +#define _ASM_KEXEC_H
> +
> +#include <asm/stacktrace.h>
> +#include <asm/page.h>
> +
> +/* Maximum physical address we can use pages from */
> +#define KEXEC_SOURCE_MEMORY_LIMIT (-1UL)
> +/* Maximum address we can reach in physical address mode */
> +#define KEXEC_DESTINATION_MEMORY_LIMIT (-1UL)
> + /* Maximum address we can use for the control code buffer */
> +#define KEXEC_CONTROL_MEMORY_LIMIT (-1UL)
> +
> +/* Reserve a page for the control code buffer */
> +#define KEXEC_CONTROL_PAGE_SIZE PAGE_SIZE
> +
> +/* The native architecture */
> +#define KEXEC_ARCH KEXEC_ARCH_LOONGARCH
> +
> +static inline void crash_setup_regs(struct pt_regs *newregs,
> +                                   struct pt_regs *oldregs)
> +{
> +       if (oldregs)
> +               memcpy(newregs, oldregs, sizeof(*newregs));
> +       else
> +               prepare_frametrace(newregs);
> +}
> +
> +#define ARCH_HAS_KIMAGE_ARCH
> +
> +struct kimage_arch {
> +       unsigned long boot_flag;
> +       unsigned long fdt_addr;
> +};
I prefer to change boot_flag to efi_boot, the latter is better to
correspond the current usage, and keeps consistency with efistub.

> +
> +typedef void (*do_kexec_t)(unsigned long boot_flag,
> +                          unsigned long fdt_addr,
> +                          unsigned long first_ind_entry,
> +                          unsigned long jump_addr);
I prefer change the order of jump_addr and first_ind_entry here.

> +
> +struct kimage;
> +extern const unsigned char relocate_new_kernel[];
> +extern const size_t relocate_new_kernel_size;
> +extern void kexec_reboot(void);
> +
> +#ifdef CONFIG_SMP
> +extern atomic_t kexec_ready_to_reboot;
> +extern const unsigned char kexec_smp_wait[];
> +#endif
> +
> +#endif /* !_ASM_KEXEC_H */
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index 7225916dd378..17dc8ce6b5ce 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -17,6 +17,8 @@ obj-$(CONFIG_CPU_HAS_FPU)     += fpu.o
>  obj-$(CONFIG_MODULES)          += module.o module-sections.o
>  obj-$(CONFIG_STACKTRACE)       += stacktrace.o
>
> +obj-$(CONFIG_KEXEC)             += machine_kexec.o relocate_kernel.o
> +
>  obj-$(CONFIG_PROC_FS)          += proc.o
>
>  obj-$(CONFIG_SMP)              += smp.o
> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
> index eb3f641d5915..0f786d670e66 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -20,7 +20,12 @@
>
>  _head:
>         .word   MZ_MAGIC                /* "MZ", MS-DOS header */
> -       .org    0x3c                    /* 0x04 ~ 0x3b reserved */
> +       .org    0x8
> +       .quad   0                       /* Image load offset from start of RAM */
> +       .dword  _end - _text            /* Effective size of kernel image */
> +       .quad   0
> +       .dword  kernel_entry            /* Kernel entry point */
> +       .org    0x3c                    /* 0x28 ~ 0x3b reserved */
>         .long   pe_header - _head       /* Offset to the PE header */
As discussed before, I prefer kernel entry point before kernel image size.

>
>  pe_header:
> diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
> new file mode 100644
> index 000000000000..7b3fea506c6d
> --- /dev/null
> +++ b/arch/loongarch/kernel/machine_kexec.c
> @@ -0,0 +1,188 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * machine_kexec.c for kexec
> + *
> + * Copyright (C) 2022 Loongson Technology Corporation Limited
> + */
> +#include <linux/compiler.h>
> +#include <linux/cpu.h>
> +#include <linux/kexec.h>
> +#include <linux/mm.h>
> +#include <linux/delay.h>
> +#include <linux/libfdt.h>
> +#include <linux/of_fdt.h>
> +
> +#include <asm/bootinfo.h>
> +#include <asm/cacheflush.h>
> +#include <asm/page.h>
> +
> +/* 0x100000 ~ 0x200000 is safe */
> +#define KEXEC_CTRL_CODE        TO_CACHE(0x100000UL)
> +#define KEXEC_BLOB_ADDR        TO_CACHE(0x108000UL)
> +
> +static unsigned long reboot_code_buffer;
> +
> +#ifdef CONFIG_SMP
> +static void (*relocated_kexec_smp_wait)(void *);
> +atomic_t kexec_ready_to_reboot = ATOMIC_INIT(0);
> +#endif
> +
> +static unsigned long jump_addr;
> +static unsigned long first_ind_entry;
> +static unsigned long boot_flag;
> +static unsigned long fdt_addr;
Keep the same order as do_kexec() may be better.

> +
> +static void kexec_image_info(const struct kimage *kimage)
> +{
> +       unsigned long i;
> +
> +       pr_debug("kexec kimage info:\n");
> +       pr_debug("\ttype:        %d\n", kimage->type);
> +       pr_debug("\tstart:       %lx\n", kimage->start);
> +       pr_debug("\thead:        %lx\n", kimage->head);
> +       pr_debug("\tnr_segments: %lu\n", kimage->nr_segments);
> +
> +       for (i = 0; i < kimage->nr_segments; i++) {
> +               pr_debug("\t    segment[%lu]: %016lx - %016lx", i,
> +                       kimage->segment[i].mem,
> +                       kimage->segment[i].mem + kimage->segment[i].memsz);
> +               pr_debug("\t\t0x%lx bytes, %lu pages\n",
> +                       (unsigned long)kimage->segment[i].memsz,
> +                       (unsigned long)kimage->segment[i].memsz /  PAGE_SIZE);
> +       }
> +}
> +
> +int machine_kexec_prepare(struct kimage *kimage)
> +{
> +       int i;
> +       void *dtb = (void *)KEXEC_BLOB_ADDR;
> +
> +       kexec_image_info(kimage);
> +
> +       /* Find the Flattened Device Tree */
> +       for (i = 0; i < kimage->nr_segments; i++) {
> +               if (!fdt_check_header(kimage->segment[i].buf)) {
> +                       memcpy(dtb, kimage->segment[i].buf, SZ_64K);
> +                       kimage->arch.boot_flag = fw_arg0;
> +                       kimage->arch.fdt_addr = (unsigned long) dtb;
> +                       break;
> +               }
> +               continue;
> +       }
> +
> +       /* kexec need a safe page to save reboot_code_buffer */
> +       kimage->control_code_page = virt_to_page((void *)KEXEC_CTRL_CODE);
> +
> +       reboot_code_buffer =
> +         (unsigned long)page_address(kimage->control_code_page);
> +       memcpy((void *)reboot_code_buffer, relocate_new_kernel,
> +              relocate_new_kernel_size);
> +
> +#ifdef CONFIG_SMP
> +       /* All secondary cpus now may jump to kexec_smp_wait cycle */
> +       relocated_kexec_smp_wait = reboot_code_buffer +
> +               (void *)(kexec_smp_wait - relocate_new_kernel);
> +#endif
> +
> +       return 0;
> +}
> +
> +void machine_kexec_cleanup(struct kimage *kimage)
> +{
> +}
> +
> +void kexec_reboot(void)
> +{
> +       do_kexec_t do_kexec = NULL;
> +
The old implementation has an "ibar" here, I suppose it is still needed?

> +#ifdef CONFIG_SMP
> +       /* All secondary cpus go to kexec_smp_wait */
> +       if (smp_processor_id() > 0) {
> +               relocated_kexec_smp_wait(NULL);
> +               unreachable();
> +       }
> +#endif
> +
> +       do_kexec = (void *)reboot_code_buffer;
> +       do_kexec(boot_flag, fdt_addr, first_ind_entry, jump_addr);
> +
> +       unreachable();
> +}
> +
> +
> +#ifdef CONFIG_SMP
> +static void kexec_shutdown_secondary(void *)
> +{
> +       local_irq_disable();
> +       while (!atomic_read(&kexec_ready_to_reboot))
> +               cpu_relax();
> +
> +       kexec_reboot();
The old implementation has an unreachable() after kexec_reboot(), but
I don't know whether it is really needed.

> +}
> +#endif
> +
> +void machine_crash_shutdown(struct pt_regs *regs)
> +{
> +}
> +
> +void machine_shutdown(void)
> +{
> +#ifdef CONFIG_SMP
> +       smp_call_function(kexec_shutdown_secondary, NULL, 0);
> +#endif
> +}
> +
> +void machine_kexec(struct kimage *image)
> +{
> +       unsigned long entry;
> +       unsigned long *ptr;
> +       struct kimage_arch *internal = &image->arch;
> +
> +       boot_flag = internal->boot_flag;
> +       fdt_addr = internal->fdt_addr;
> +
> +       jump_addr = (unsigned long)phys_to_virt(image->start);
> +
> +       first_ind_entry = (unsigned long)phys_to_virt(image->head & PAGE_MASK);
> +
> +       /*
> +        * The generic kexec code builds a page list with physical
> +        * addresses. they are directly accessible through XKPRANGE
> +        * hence the phys_to_virt() call.
> +        */
> +       for (ptr = &image->head; (entry = *ptr) && !(entry & IND_DONE);
> +            ptr = (entry & IND_INDIRECTION) ?
> +              phys_to_virt(entry & PAGE_MASK) : ptr + 1) {
> +               if (*ptr & IND_SOURCE || *ptr & IND_INDIRECTION ||
> +                   *ptr & IND_DESTINATION)
> +                       *ptr = (unsigned long) phys_to_virt(*ptr);
> +       }
> +
> +       /* Mark offline before disabling local irq. */
> +       set_cpu_online(smp_processor_id(), false);
> +
> +       /* we do not want to be bothered. */
> +       local_irq_disable();
> +
> +       pr_notice("Will call new kernel at %lx\n", jump_addr);
> +       pr_notice("FDT image at %lx\n", fdt_addr);
> +       pr_notice("Bye ...\n");
> +
> +       /* Make reboot code buffer available to the boot CPU. */
> +       flush_cache_all();
> +
> +#ifdef CONFIG_SMP
> +       atomic_set(&kexec_ready_to_reboot, 1);
> +#endif
> +
> +       /*
> +        * We know we were online, and there will be no incoming IPIs at
> +        * this point.
> +        */
> +       set_cpu_online(smp_processor_id(), true);
> +
> +       /* Ensure remote CPUs observe that we're online before rebooting. */
> +       smp_mb__after_atomic();
> +
> +       kexec_reboot();
> +}
> diff --git a/arch/loongarch/kernel/relocate_kernel.S b/arch/loongarch/kernel/relocate_kernel.S
> new file mode 100644
> index 000000000000..05a0c1ccfab6
> --- /dev/null
> +++ b/arch/loongarch/kernel/relocate_kernel.S
> @@ -0,0 +1,106 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * relocate_kernel.S for kexec
> + *
> + * Copyright (C) 2022 Loongson Technology Corporation Limited
> + */
> +
> +#include <linux/kexec.h>
> +
> +#include <asm/asm.h>
> +#include <asm/asmmacro.h>
> +#include <asm/regdef.h>
> +#include <asm/loongarch.h>
> +#include <asm/stackframe.h>
> +#include <asm/addrspace.h>
> +
> +SYM_CODE_START(relocate_new_kernel)
> +       /*
> +        * s0: Boot flag passed to the new kernel
> +        * s1: Virt address of the FDT image
> +        * s2: Pointer to the current entry
"Pointer to the current entry" can be "Pointer to the current
indirection page entry"? And I think we needn't backup Ax to Sx except
this one in the assembly below.

Huacai

> +        * s3: Virt address to jump to after relocation
> +        */
> +       move            s0, a0
> +       move            s1, a1
> +       move            s2, a2
> +       move            s3, a3
> +
> +process_entry:
> +       PTR_L           s4, s2, 0
> +       PTR_ADDI        s2, s2, SZREG
> +
> +       /* destination page */
> +       andi            s5, s4, IND_DESTINATION
> +       beqz            s5, 1f
> +       li.w            t0, ~0x1
> +       and             s6, s4, t0      /* store destination addr in s6 */
> +       b               process_entry
> +
> +1:
> +       /* indirection page, update s2  */
> +       andi            s5, s4, IND_INDIRECTION
> +       beqz            s5, 1f
> +       li.w            t0, ~0x2
> +       and             s2, s4, t0
> +       b               process_entry
> +
> +1:
> +       /* done page */
> +       andi            s5, s4, IND_DONE
> +       beqz            s5, 1f
> +       b               done
> +1:
> +       /* source page */
> +       andi            s5, s4, IND_SOURCE
> +       beqz            s5, process_entry
> +       li.w            t0, ~0x8
> +       and             s4, s4, t0
> +       li.w            s8, (1 << _PAGE_SHIFT) / SZREG
> +
> +copy_word:
> +       /* copy page word by word */
> +       REG_L           s7, s4, 0
> +       REG_S           s7, s6, 0
> +       PTR_ADDI        s6, s6, SZREG
> +       PTR_ADDI        s4, s4, SZREG
> +       LONG_ADDI       s8, s8, -1
> +       beqz            s8, process_entry
> +       b               copy_word
> +       b               process_entry
> +
> +done:
> +       ibar            0
> +       dbar            0
> +
> +       move            a0, s0
> +       move            a1, s1
> +       /* jump to the new kernel */
> +       jr              s3
> +SYM_CODE_END(relocate_new_kernel)
> +
> +#ifdef CONFIG_SMP
> +/*
> + * Other CPUs should wait until code is relocated and
> + * then start at entry (?) point.
> + */
> +SYM_CODE_START(kexec_smp_wait)
> +1:     li.w            t0, 0x100                       /* wait for init loop */
> +2:     addi.w          t0, t0, -1                      /* limit mailbox access */
> +       bnez            t0, 2b
> +       li.w            t1, LOONGARCH_IOCSR_MBUF0
> +       iocsrrd.w       s1, t1                          /* check PC as an indicator */
> +       beqz            s1, 1b
> +       iocsrrd.d       s1, t1                          /* get PC via mailbox */
> +
> +       li.d            t0, CACHE_BASE
> +       or              s1, s1, t0                      /* s1 = TO_CACHE(s1) */
> +       jr              s1                              /* jump to initial PC */
> +SYM_CODE_END(kexec_smp_wait)
> +#endif
> +
> +relocate_new_kernel_end:
> +
> +SYM_DATA_START(relocate_new_kernel_size)
> +       PTR             relocate_new_kernel_end - relocate_new_kernel
> +SYM_DATA_END(relocate_new_kernel_size)
> --
> 2.36.0
>