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

[Youling Tang <tangyouling@loongson.cn>]

On 08/30/2022 11:25 AM, Youling Tang wrote:
> Hi, Jinyang
>
> On 08/30/2022 09:53 AM, Jinyang He wrote:
>> Hi, Youling,
>>
>>
>> On 08/29/2022 12:37 PM, Youling Tang 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@loongson.cn>
>>> ---
>>>   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   | 178 ++++++++++++++++++++++++
>>>   arch/loongarch/kernel/relocate_kernel.S | 125 +++++++++++++++++
>>>   6 files changed, 380 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 45364cffc793..903c82fa958d 100644
>>> --- a/arch/loongarch/Kconfig
>>> +++ b/arch/loongarch/Kconfig
>>> @@ -409,6 +409,17 @@ config FORCE_MAX_ZONEORDER
>>>         The page size is not necessarily 4KB.  Keep this in mind
>>>         when choosing a value for this option.
>>>   +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..5c9e7b5eccb8
>>> --- /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;
>>> +};
>>> +
>>> +typedef void (*do_kexec_t)(unsigned long boot_flag,
>>> +               unsigned long fdt_addr,
>>> +               unsigned long first_ind_entry,
>>> +               unsigned long jump_addr);
>>> +
>>> +struct kimage;
>>> +extern const unsigned char relocate_new_kernel[];
>>> +extern const size_t relocate_new_kernel_size;
>>> +
>>> +#ifdef CONFIG_SMP
>>> +extern atomic_t kexec_ready_to_reboot;
>>> +extern const unsigned char kexec_smp_wait[];
>>> +extern void kexec_reboot(void);
>>> +#endif
>>> +
>>> +#endif /* !_ASM_KEXEC_H */
>>> diff --git a/arch/loongarch/kernel/Makefile
>>> b/arch/loongarch/kernel/Makefile
>>> index a213e994db68..20b64ac3f128 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 01bac62a6442..22bdf4928325 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 */
>>>     pe_header:
>>> diff --git a/arch/loongarch/kernel/machine_kexec.c
>>> b/arch/loongarch/kernel/machine_kexec.c
>>> new file mode 100644
>>> index 000000000000..4ffcd4cd9c8c
>>> --- /dev/null
>>> +++ b/arch/loongarch/kernel/machine_kexec.c
>>> @@ -0,0 +1,178 @@
>>> +// 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
>>> +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;
>>> +
>>> +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);
>> It copys same content to KEXEC_CTRL_CODE each time, could we do this at
>> boot time?
> I think it's possible to have the copy action happen at boot-time or
> during the prepare phase. (RISCV in prepare, MIPS in boot-time)
>
>>
>> BTW, our system always keep the low-2MB no used, on mips-loongson or
>> LoongArch. Is that necessary on LoongArch? We cannot use parameter
>> 'mem=YYM' normally but 'mem=YYM@2M' is ok. And the low-2MB is not
>> in virtual memory management, although we can get it in kernel.
> For existing kernels, the low 2M has been reserved by
> memblock_reserve(PHYS_OFFSET, 0x200000), maybe it is acceptable to keep
> the low 2M behavior.
>
> Yes, we need to use "mem=YM@2M" if the low 2M is reserved.
>
>>
>> In kexec/kdump process, we can follows kimage_alloc_control_pages().
>> When the boot cpu copy complete the second-kernels, all cpus can jump
>> to a kernel-entry-trampoline which is in kernel image. Then we don't
>> worry about the code can be destroyed. The kernel-entry-trampoline
>> get its cpuid, keep non-boot cpus do as kexec_smp_wait and let boot
>> cpu go kernel-entry. In this way we can drop the low-2MB IMO.
>
> It is also feasible to dynamically allocate control pages, but it is
> easier to use a low 2M approach. What do you think, Huacai?
>
>>
>>> +
>>> +    /* 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);
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +void machine_kexec_cleanup(struct kimage *kimage)
>>> +{
>>> +}
>>> +
>>> +#ifdef CONFIG_SMP
>>> +void kexec_reboot(void)
>>> +{
>>> +    do_kexec_t do_kexec = NULL;
>>> +
>>> +    /* All secondary cpus go to kexec_smp_wait */
>>> +    if (smp_processor_id() > 0) {
>>> +        relocated_kexec_smp_wait(NULL);
>>> +        unreachable();
>>> +    }
>>> +
>>> +    do_kexec = (void *)reboot_code_buffer;
>>> +    do_kexec(boot_flag, fdt_addr, first_ind_entry, jump_addr);
>>> +
>>> +    unreachable();
>>> +}
>>> +
>>> +static void kexec_shutdown_secondary(void *)
>>> +{
>>> +    local_irq_disable();
>>> +    while (!atomic_read(&kexec_ready_to_reboot))
>>> +        cpu_relax();
>>> +
>>> +    kexec_reboot();
>>> +}
>>> +
>>> +void machine_crash_shutdown(struct pt_regs *regs)
>>> +{
>>> +}
>>> +#endif
>>> +
>>> +void machine_shutdown(void)
>>> +{
>>> +    smp_call_function(kexec_shutdown_secondary, NULL, 0);
>>> +}
>>> +
>>> +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();
>>> +
>>> +    atomic_set(&kexec_ready_to_reboot, 1);
>>> +
>>> +    /*
>>> +     * 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..d1f242f74ea8
>>> --- /dev/null
>>> +++ b/arch/loongarch/kernel/relocate_kernel.S
>>> @@ -0,0 +1,125 @@
>>> +/* 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>
>>> +
>>> +#define IPI_REG_BASE 0x1fe01000
>>> +
>>> +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
>>> +     * 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:
>>> +    dbar        0
>> ibar, too?
>
> Will add ibar 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)
>>> +    li.d        t0, IPI_REG_BASE
>>> +    li.d        t1, UNCACHE_BASE
>>> +    or        t0, t0, t1
>>> +
>>> +    /*
>>> +     * s1:initfn
>>> +     * t0:base t1:cpuid t2:node t3:core t4:count
>>> +     */
>>> +    csrrd        t1, LOONGARCH_CSR_CPUID
>>> +    andi        t1, t1, CSR_CPUID_COREID
>>> +    andi        t3, t1, 0x3
>>> +    slli.w        t3, t3, 8              /* get core id */
>>> +    or        t0, t0, t3
>>> +    andi        t2, t1, 0x3c
>>> +    slli.d        t2, t2, 42             /* get node id */
>>> +    or        t0, t0, t2
>>> +
>>> +1:    li.w        t4, 0x100              /* wait for init loop */
>>> +2:    addi.w        t4, t4, -1             /* limit mailbox access */
>>> +    bnez        t4, 2b
>>> +    ld.w        s1, t0, 0x20           /* check PC as an indicator */
>> Can we do this with iocsr*?
>
> OK, I will consider the implementation in the iocsr way.
>

The kexec_smp_wait implementation will be modified in the next release
as follows：

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
         jr              s1                              /* jump to 
initial PC */
SYM_CODE_END(kexec_smp_wait)

1) Using the iocsr method
2) Remove sp, tp settings. sp, tp will be obtained from cpuboot_data in
smpboot_entry.

Thanks again Jinyang for the suggestion.


Youling.

> Thanks,
> Youling
>>
>> Thanks,
>> Jinyang
>>> +    beqz        s1, 1b
>>> +    ld.d        s1, t0, 0x20           /* get PC via mailbox */
>>> +    ld.d        sp, t0, 0x28           /* get SP via mailbox */
>>> +    ld.d        tp, t0, 0x30           /* get TP via mailbox */
>>> +
>>> +    li.d        t0, CACHE_BASE
>>> +    or        s1, s1, t0
>>> +    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)
>>
>


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