Date:   Sun, 4 Sep 2022 20:21:21 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Youling Tang <tangyouling@...ngson.cn>
Cc:     Baoquan He <bhe@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        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,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] LoongArch: Add kdump support

Hi, Youling,

I think crash.c can be merged into crash_dump.c

Huacai

On Mon, Aug 29, 2022 at 12:37 PM Youling Tang <tangyouling@...ngson.cn> wrote:
>
> This patch adds support for kdump, the kernel will reserve a region
> for the crash kernel and jump there on panic.
>
> Arch-specific functions are added to allow for implementing a crash
> dump file interface, /proc/vmcore, which can be viewed as a ELF file.
>
> A user space tool, like kexec-tools, is responsible for allocating a
> separate region for the core's ELF header within crash kdump kernel
> memory and filling it in when executing kexec_load().
>
> Then, its location will be advertised to crash dump kernel via a new
> device-tree property, "linux,elfcorehdr", and crash dump kernel preserves
> the region for later use with fdt_reserve_elfcorehdr() at boot time.
>
> At the same time, it will also limit the crash kdump kernel to the
> crashkernel area via a new device-tree property, "linux, usable-memory-range",
> so as not to destroy the original kernel dump data.
>
> On crash dump kernel, /proc/vmcore will access the primary kernel's memory
> with copy_oldmem_page().
>
> I tested this on  LoongArch 3A5000 machine and works as expected (Suggest
> crashkernel parameter is "crashkernel=512M@...0M"), you may test it by
> triggering a crash through /proc/sysrq_trigger:
>
>  $ sudo kexec -p /boot/vmlinux-kdump --reuse-cmdline --append="nr_cpus=1"
>  # echo c > /proc/sysrq_trigger
>
> Signed-off-by: Youling Tang <tangyouling@...ngson.cn>
> ---
>  arch/loongarch/Kconfig                  |  22 ++++++
>  arch/loongarch/Makefile                 |   4 +
>  arch/loongarch/kernel/Makefile          |   3 +-
>  arch/loongarch/kernel/crash.c           | 100 ++++++++++++++++++++++++
>  arch/loongarch/kernel/crash_dump.c      |  19 +++++
>  arch/loongarch/kernel/machine_kexec.c   |  12 ++-
>  arch/loongarch/kernel/mem.c             |   6 ++
>  arch/loongarch/kernel/relocate_kernel.S |   6 ++
>  arch/loongarch/kernel/setup.c           |  49 ++++++++++++
>  arch/loongarch/kernel/traps.c           |   4 +
>  10 files changed, 217 insertions(+), 8 deletions(-)
>  create mode 100644 arch/loongarch/kernel/crash.c
>  create mode 100644 arch/loongarch/kernel/crash_dump.c
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 903c82fa958d..7c1b07a5b5bd 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -420,6 +420,28 @@ config KEXEC
>
>           The name comes from the similarity to the exec system call.
>
> +config CRASH_DUMP
> +       bool "Build kdump crash kernel"
> +       help
> +         Generate crash dump after being started by kexec. This should
> +         be normally only set in special crash dump kernels which are
> +         loaded in the main kernel with kexec-tools into a specially
> +         reserved region and then later executed after a crash by
> +         kdump/kexec.
> +
> +         For more details see Documentation/admin-guide/kdump/kdump.rst
> +
> +config PHYSICAL_START
> +       hex "Physical address where the kernel is loaded"
> +       default "0x9000000091000000" if 64BIT
> +       depends on CRASH_DUMP
> +       help
> +         This gives the XKPRANGE address where the kernel is loaded.
> +         If you plan to use kernel for capturing the crash dump change
> +         this value to start of the reserved region (the "X" value as
> +         specified in the "crashkernel=YM@XM" command line boot parameter
> +         passed to the panic-ed kernel).
> +
>  config SECCOMP
>         bool "Enable seccomp to safely compute untrusted bytecode"
>         depends on PROC_FS
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index 4bc47f47cfd8..7dabd580426d 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -48,7 +48,11 @@ KBUILD_CFLAGS_MODULE         += -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs
>  cflags-y += -ffreestanding
>  cflags-y += $(call cc-option, -mno-check-zero-division)
>
> +ifdef CONFIG_PHYSICAL_START
> +load-y         = $(CONFIG_PHYSICAL_START)
> +else
>  load-y         = 0x9000000000200000
> +endif
>  bootvars-y     = VMLINUX_LOAD_ADDRESS=$(load-y)
>
>  drivers-$(CONFIG_PCI)          += arch/loongarch/pci/
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index 20b64ac3f128..df5aea129364 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -17,7 +17,8 @@ obj-$(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_KEXEC)             += machine_kexec.o relocate_kernel.o crash.o
> +obj-$(CONFIG_CRASH_DUMP)        += crash_dump.o
>
>  obj-$(CONFIG_PROC_FS)          += proc.o
>
> diff --git a/arch/loongarch/kernel/crash.c b/arch/loongarch/kernel/crash.c
> new file mode 100644
> index 000000000000..b4f249ec6301
> --- /dev/null
> +++ b/arch/loongarch/kernel/crash.c
> @@ -0,0 +1,100 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Loongson Technology Corporation Limited
> + *
> + * Derived from MIPS
> + */
> +#include <linux/kernel.h>
> +#include <linux/smp.h>
> +#include <linux/reboot.h>
> +#include <linux/crash_dump.h>
> +#include <linux/delay.h>
> +#include <linux/irq.h>
> +#include <linux/types.h>
> +#include <linux/sched.h>
> +#include <linux/sched/task_stack.h>
> +#include <asm/cacheflush.h>
> +#include <asm/kexec.h>
> +
> +static cpumask_t cpus_in_crash = CPU_MASK_NONE;
> +
> +#ifdef CONFIG_SMP
> +static void crash_shutdown_secondary(void *passed_regs)
> +{
> +       struct pt_regs *regs = passed_regs;
> +       int cpu = smp_processor_id();
> +
> +       /*
> +        * If we are passed registers, use those.  Otherwise get the
> +        * regs from the last interrupt, which should be correct, as
> +        * we are in an interrupt.  But if the regs are not there,
> +        * pull them from the top of the stack.  They are probably
> +        * wrong, but we need something to keep from crashing again.
> +        */
> +       if (!regs)
> +               regs = get_irq_regs();
> +       if (!regs)
> +               regs = task_pt_regs(current);
> +
> +       local_irq_disable();
> +       if (!cpumask_test_cpu(cpu, &cpus_in_crash))
> +               crash_save_cpu(regs, cpu);
> +       cpumask_set_cpu(cpu, &cpus_in_crash);
> +
> +       while (!atomic_read(&kexec_ready_to_reboot))
> +               cpu_relax();
> +
> +       kexec_reboot();
> +}
> +
> +/* Override the weak function in kernel/panic.c */
> +void crash_smp_send_stop(void)
> +{
> +       static int cpus_stopped;
> +       unsigned long timeout;
> +       unsigned int ncpus;
> +
> +       /*
> +        * This function can be called twice in panic path, but obviously
> +        * we execute this only once.
> +        */
> +       if (cpus_stopped)
> +               return;
> +
> +       cpus_stopped = 1;
> +
> +        /* Excluding the panic cpu */
> +       ncpus = num_online_cpus() - 1;
> +
> +       smp_call_function(crash_shutdown_secondary, NULL, 0);
> +       smp_wmb();
> +
> +       /*
> +        * The crash CPU sends an IPI and wait for other CPUs to
> +        * respond. Delay of at least 10 seconds.
> +        */
> +       pr_emerg("Sending IPI to other cpus...\n");
> +       timeout = USEC_PER_SEC * 10;
> +       while ((cpumask_weight(&cpus_in_crash) < ncpus) && timeout--) {
> +               cpu_relax();
> +               udelay(1);
> +       }
> +}
> +
> +#endif
> +
> +void machine_crash_shutdown(struct pt_regs *regs)
> +{
> +       int crashing_cpu;
> +
> +       local_irq_disable();
> +
> +       crashing_cpu = smp_processor_id();
> +       crash_save_cpu(regs, crashing_cpu);
> +
> +       /* shutdown non-crashing cpus */
> +       crash_smp_send_stop();
> +       cpumask_set_cpu(crashing_cpu, &cpus_in_crash);
> +
> +       pr_info("Starting crashdump kernel...\n");
> +}
> diff --git a/arch/loongarch/kernel/crash_dump.c b/arch/loongarch/kernel/crash_dump.c
> new file mode 100644
> index 000000000000..13e5d2f7870d
> --- /dev/null
> +++ b/arch/loongarch/kernel/crash_dump.c
> @@ -0,0 +1,19 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/highmem.h>
> +#include <linux/crash_dump.h>
> +#include <linux/io.h>
> +
> +ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
> +                        size_t csize, unsigned long offset)
> +{
> +       void  *vaddr;
> +
> +       if (!csize)
> +               return 0;
> +
> +       vaddr = kmap_local_pfn(pfn);
> +       csize = copy_to_iter(vaddr + offset, csize, iter);
> +       kunmap_local(vaddr);
> +
> +       return csize;
> +}
> diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
> index 4ffcd4cd9c8c..f793a3ff09a3 100644
> --- a/arch/loongarch/kernel/machine_kexec.c
> +++ b/arch/loongarch/kernel/machine_kexec.c
> @@ -69,7 +69,7 @@ int machine_kexec_prepare(struct kimage *kimage)
>                 continue;
>         }
>
> -       /* kexec need a safe page to save reboot_code_buffer */
> +       /* kexec/kdump need a safe page to save reboot_code_buffer */
>         kimage->control_code_page = virt_to_page((void *)KEXEC_CTRL_CODE);
>
>         reboot_code_buffer =
> @@ -113,10 +113,6 @@ static void kexec_shutdown_secondary(void *)
>
>         kexec_reboot();
>  }
> -
> -void machine_crash_shutdown(struct pt_regs *regs)
> -{
> -}
>  #endif
>
>  void machine_shutdown(void)
> @@ -135,7 +131,8 @@ void machine_kexec(struct kimage *image)
>
>         jump_addr = (unsigned long)phys_to_virt(image->start);
>
> -       first_ind_entry = (unsigned long)phys_to_virt(image->head & PAGE_MASK);
> +       if (image->type == KEXEC_TYPE_DEFAULT)
> +               first_ind_entry = (unsigned long)phys_to_virt(image->head & PAGE_MASK);
>
>         /*
>          * The generic kexec code builds a page list with physical
> @@ -167,7 +164,8 @@ void machine_kexec(struct kimage *image)
>
>         /*
>          * We know we were online, and there will be no incoming IPIs at
> -        * this point.
> +        * this point. Mark online again before rebooting so that the crash
> +        * analysis tool will see us correctly.
>          */
>         set_cpu_online(smp_processor_id(), true);
>
> diff --git a/arch/loongarch/kernel/mem.c b/arch/loongarch/kernel/mem.c
> index 7423361b0ebc..c6def6ff81c8 100644
> --- a/arch/loongarch/kernel/mem.c
> +++ b/arch/loongarch/kernel/mem.c
> @@ -5,6 +5,7 @@
>  #include <linux/efi.h>
>  #include <linux/initrd.h>
>  #include <linux/memblock.h>
> +#include <linux/of_fdt.h>
>
>  #include <asm/bootinfo.h>
>  #include <asm/loongson.h>
> @@ -61,4 +62,9 @@ void __init memblock_init(void)
>
>         /* Reserve the initrd */
>         reserve_initrd_mem();
> +
> +       /* Mainly reserved memory for the elf core head */
> +       early_init_fdt_scan_reserved_mem();
> +       /* Parse linux,usable-memory-range is for crash dump kernel */
> +       early_init_dt_check_for_usable_mem_range();
>  }
> diff --git a/arch/loongarch/kernel/relocate_kernel.S b/arch/loongarch/kernel/relocate_kernel.S
> index d1f242f74ea8..4ee5ac4ac2d7 100644
> --- a/arch/loongarch/kernel/relocate_kernel.S
> +++ b/arch/loongarch/kernel/relocate_kernel.S
> @@ -28,6 +28,12 @@ SYM_CODE_START(relocate_new_kernel)
>         move            s2, a2
>         move            s3, a3
>
> +       /*
> +        * In case of a kdump/crash kernel, the indirection page is not
> +        * populated as the kernel is directly copied to a reserved location
> +        */
> +       beqz            s2, done
> +
>  process_entry:
>         PTR_L           s4, s2, 0
>         PTR_ADDI        s2, s2, SZREG
> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> index f938aae3e92c..ea34b77e402f 100644
> --- a/arch/loongarch/kernel/setup.c
> +++ b/arch/loongarch/kernel/setup.c
> @@ -19,6 +19,8 @@
>  #include <linux/memblock.h>
>  #include <linux/initrd.h>
>  #include <linux/ioport.h>
> +#include <linux/kexec.h>
> +#include <linux/crash_dump.h>
>  #include <linux/root_dev.h>
>  #include <linux/console.h>
>  #include <linux/pfn.h>
> @@ -186,6 +188,50 @@ static int __init early_parse_mem(char *p)
>  }
>  early_param("mem", early_parse_mem);
>
> +static void __init loongarch_parse_crashkernel(void)
> +{
> +#ifdef CONFIG_KEXEC
> +       unsigned long long start;
> +       unsigned long long total_mem;
> +       unsigned long long crash_size, crash_base;
> +       int ret;
> +
> +       total_mem = memblock_phys_mem_size();
> +       ret = parse_crashkernel(boot_command_line, total_mem,
> +                               &crash_size, &crash_base);
> +       if (ret != 0 || crash_size <= 0)
> +               return;
> +
> +
> +       start = memblock_phys_alloc_range(crash_size, 1, crash_base,
> +                                       crash_base + crash_size);
> +       if (start != crash_base) {
> +               pr_warn("Invalid memory region reserved for crash kernel\n");
> +               return;
> +       }
> +
> +       crashk_res.start = crash_base;
> +       crashk_res.end   = crash_base + crash_size - 1;
> +#endif
> +}
> +
> +static void __init request_crashkernel(struct resource *res)
> +{
> +#ifdef CONFIG_KEXEC
> +       int ret;
> +
> +       if (crashk_res.start == crashk_res.end)
> +               return;
> +
> +       ret = request_resource(res, &crashk_res);
> +       if (!ret)
> +               pr_info("Reserving %ldMB of memory at %ldMB for crashkernel\n",
> +                       (unsigned long)((crashk_res.end -
> +                                        crashk_res.start + 1) >> 20),
> +                       (unsigned long)(crashk_res.start  >> 20));
> +#endif
> +}
> +
>  void __init platform_init(void)
>  {
>         efi_init();
> @@ -229,6 +275,8 @@ static void __init arch_mem_init(char **cmdline_p)
>
>         check_kernel_sections_mem();
>
> +       loongarch_parse_crashkernel();
> +
>         /*
>          * In order to reduce the possibility of kernel panic when failed to
>          * get IO TLB memory under CONFIG_SWIOTLB, it is better to allocate
> @@ -290,6 +338,7 @@ static void __init resource_init(void)
>                 request_resource(res, &code_resource);
>                 request_resource(res, &data_resource);
>                 request_resource(res, &bss_resource);
> +               request_crashkernel(res);
>         }
>  }
>
> diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
> index aa1c95aaf595..0e610872f3f4 100644
> --- a/arch/loongarch/kernel/traps.c
> +++ b/arch/loongarch/kernel/traps.c
> @@ -10,6 +10,7 @@
>  #include <linux/entry-common.h>
>  #include <linux/init.h>
>  #include <linux/kernel.h>
> +#include <linux/kexec.h>
>  #include <linux/module.h>
>  #include <linux/extable.h>
>  #include <linux/mm.h>
> @@ -246,6 +247,9 @@ void __noreturn die(const char *str, struct pt_regs *regs)
>
>         oops_exit();
>
> +       if (regs && kexec_should_crash(current))
> +               crash_kexec(regs);
> +
>         if (in_interrupt())
>                 panic("Fatal exception in interrupt");
>
> --
> 2.36.0
>

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