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SubjectRe: [PATCH 1/3] LoongArch: Add kexec support
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On 08/30/2022 11:42 AM, Huacai Chen wrote:

> On Tue, Aug 30, 2022 at 11:26 AM Youling Tang <tangyouling@loongson.cn> 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?
> I prefer to use the low 2MB.
>
> Huacai
Low 2MB also is ok for me, like a trick. And should it free
control_code_page here?

>>>> +
>>>> + /* 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.
>>
>> 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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