Message-ID: <e981e841-c43c-bbc5-a0f9-1077be9811cb@loongson.cn>
Date:   Tue, 30 Aug 2022 09:53:09 +0800
From:   Jinyang He <hejinyang@...ngson.cn>
To:     Youling Tang <tangyouling@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>,
        Baoquan He <bhe@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>
Cc:     WANG Xuerui <kernel@...0n.name>, Vivek Goyal <vgoyal@...hat.com>,
        Dave Young <dyoung@...hat.com>, Guo Ren <guoren@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        kexec@...ts.infradead.org, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] LoongArch: Add kexec support

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@...ngson.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?

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.

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.

> +
> +	/* 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?
> +
> +	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*?

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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