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From:   Alex Ghiti <alex@ghiti.fr>
Subject: Re: [PATCH v3 4/5] RISC-V: Add kdump support
To:     Nick Kossifidis <mick@ics.forth.gr>,
        linux-riscv@lists.infradead.org, palmer@dabbelt.com
Cc:     paul.walmsley@sifive.com, linux-kernel@vger.kernel.org
References: <20210405085712.1953848-1-mick@ics.forth.gr>
 <20210405085712.1953848-5-mick@ics.forth.gr>
Message-ID: <1385f2a4-53a9-535b-851a-3c470f1f3bc1@ghiti.fr>
Date:   Tue, 6 Apr 2021 14:36:22 -0400
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Hi Nick,

Le 4/5/21 ? 4:57 AM, Nick Kossifidis a ?crit?:
> This patch adds support for kdump, the kernel will reserve a
> region for the crash kernel and jump there on panic. In order
> for userspace tools (kexec-tools) to prepare the crash kernel
> kexec image, we also need to expose some information on
> /proc/iomem for the memory regions used by the kernel and for
> the region reserved for crash kernel. Note that on userspace
> the device tree is used to determine the system's memory
> layout so the "System RAM" on /proc/iomem is ignored.
> 
> I tested this on riscv64 qemu and works as expected, you may
> test it by triggering a crash through /proc/sysrq_trigger:
> 
> echo c > /proc/sysrq_trigger
> 
> v3:
>   * Move ELF_CORE_COPY_REGS to asm/elf.h instead of uapi/asm/elf.h
>   * Set stvec when disabling MMU
>   * Minor cleanups and re-base
> 
> v2:
>   * Properly populate the ioresources tree, so that it can be
>     used later on for implementing strict /dev/mem.
>   * Minor cleanups and re-base
> 
> Signed-off-by: Nick Kossifidis <mick@ics.forth.gr>
> ---
>   arch/riscv/include/asm/elf.h        |  6 +++
>   arch/riscv/include/asm/kexec.h      | 19 ++++---
>   arch/riscv/kernel/Makefile          |  2 +-
>   arch/riscv/kernel/crash_save_regs.S | 56 +++++++++++++++++++++
>   arch/riscv/kernel/kexec_relocate.S  | 68 ++++++++++++++++++++++++-
>   arch/riscv/kernel/machine_kexec.c   | 43 +++++++++-------
>   arch/riscv/kernel/setup.c           | 11 ++++-
>   arch/riscv/mm/init.c                | 77 +++++++++++++++++++++++++++++
>   8 files changed, 255 insertions(+), 27 deletions(-)
>   create mode 100644 arch/riscv/kernel/crash_save_regs.S
> 
> diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
> index 5c725e1df..f4b490cd0 100644
> --- a/arch/riscv/include/asm/elf.h
> +++ b/arch/riscv/include/asm/elf.h
> @@ -81,4 +81,10 @@ extern int arch_setup_additional_pages(struct linux_binprm *bprm,
>   	int uses_interp);
>   #endif /* CONFIG_MMU */
>   
> +#define ELF_CORE_COPY_REGS(dest, regs)			\
> +do {							\
> +	*(struct user_regs_struct *)&(dest) =		\
> +		*(struct user_regs_struct *)regs;	\
> +} while (0);
> +
>   #endif /* _ASM_RISCV_ELF_H */
> diff --git a/arch/riscv/include/asm/kexec.h b/arch/riscv/include/asm/kexec.h
> index efc69feb4..4fd583acc 100644
> --- a/arch/riscv/include/asm/kexec.h
> +++ b/arch/riscv/include/asm/kexec.h
> @@ -21,11 +21,16 @@
>   
>   #define KEXEC_ARCH KEXEC_ARCH_RISCV
>   
> +extern void riscv_crash_save_regs(struct pt_regs *newregs);
> +
>   static inline void
>   crash_setup_regs(struct pt_regs *newregs,
>   		 struct pt_regs *oldregs)
>   {
> -	/* Dummy implementation for now */
> +	if (oldregs)
> +		memcpy(newregs, oldregs, sizeof(struct pt_regs));
> +	else
> +		riscv_crash_save_regs(newregs);
>   }
>   
>   
> @@ -38,10 +43,12 @@ struct kimage_arch {
>   const extern unsigned char riscv_kexec_relocate[];
>   const extern unsigned int riscv_kexec_relocate_size;
>   
> -typedef void (*riscv_kexec_do_relocate)(unsigned long first_ind_entry,
> -					unsigned long jump_addr,
> -					unsigned long fdt_addr,
> -					unsigned long hartid,
> -					unsigned long va_pa_off);
> +typedef void (*riscv_kexec_method)(unsigned long first_ind_entry,
> +				   unsigned long jump_addr,
> +				   unsigned long fdt_addr,
> +				   unsigned long hartid,
> +				   unsigned long va_pa_off);
> +
> +extern riscv_kexec_method riscv_kexec_norelocate;
>   
>   #endif
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index c2594018c..07f676ad3 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -58,7 +58,7 @@ obj-$(CONFIG_SMP) += cpu_ops_sbi.o
>   endif
>   obj-$(CONFIG_HOTPLUG_CPU)	+= cpu-hotplug.o
>   obj-$(CONFIG_KGDB)		+= kgdb.o
> -obj-${CONFIG_KEXEC}		+= kexec_relocate.o machine_kexec.o
> +obj-${CONFIG_KEXEC}		+= kexec_relocate.o crash_save_regs.o machine_kexec.o
>   
>   obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
>   
> diff --git a/arch/riscv/kernel/crash_save_regs.S b/arch/riscv/kernel/crash_save_regs.S
> new file mode 100644
> index 000000000..7832fb763
> --- /dev/null
> +++ b/arch/riscv/kernel/crash_save_regs.S
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2020 FORTH-ICS/CARV
> + *  Nick Kossifidis <mick@ics.forth.gr>
> + */
> +
> +#include <asm/asm.h>    	/* For RISCV_* and REG_* macros */
> +#include <asm/csr.h>		/* For CSR_* macros */
> +#include <asm/asm-offsets.h>	/* For offsets on pt_regs */
> +#include <linux/linkage.h>	/* For SYM_* macros */
> +
> +.section ".text"
> +SYM_CODE_START(riscv_crash_save_regs)
> +	REG_S ra,  PT_RA(a0)	/* x1 */
> +	REG_S sp,  PT_SP(a0)	/* x2 */
> +	REG_S gp,  PT_GP(a0)	/* x3 */
> +	REG_S tp,  PT_TP(a0)	/* x4 */
> +	REG_S t0,  PT_T0(a0)	/* x5 */
> +	REG_S t1,  PT_T1(a0)	/* x6 */
> +	REG_S t2,  PT_T2(a0)	/* x7 */
> +	REG_S s0,  PT_S0(a0)	/* x8/fp */
> +	REG_S s1,  PT_S1(a0)	/* x9 */
> +	REG_S a0,  PT_A0(a0)	/* x10 */
> +	REG_S a1,  PT_A1(a0)	/* x11 */
> +	REG_S a2,  PT_A2(a0)	/* x12 */
> +	REG_S a3,  PT_A3(a0)	/* x13 */
> +	REG_S a4,  PT_A4(a0)	/* x14 */
> +	REG_S a5,  PT_A5(a0)	/* x15 */
> +	REG_S a6,  PT_A6(a0)	/* x16 */
> +	REG_S a7,  PT_A7(a0)	/* x17 */
> +	REG_S s2,  PT_S2(a0)	/* x18 */
> +	REG_S s3,  PT_S3(a0)	/* x19 */
> +	REG_S s4,  PT_S4(a0)	/* x20 */
> +	REG_S s5,  PT_S5(a0)	/* x21 */
> +	REG_S s6,  PT_S6(a0)	/* x22 */
> +	REG_S s7,  PT_S7(a0)	/* x23 */
> +	REG_S s8,  PT_S8(a0)	/* x24 */
> +	REG_S s9,  PT_S9(a0)	/* x25 */
> +	REG_S s10, PT_S10(a0)	/* x26 */
> +	REG_S s11, PT_S11(a0)	/* x27 */
> +	REG_S t3,  PT_T3(a0)	/* x28 */
> +	REG_S t4,  PT_T4(a0)	/* x29 */
> +	REG_S t5,  PT_T5(a0)	/* x30 */
> +	REG_S t6,  PT_T6(a0)	/* x31 */
> +
> +	csrr t1, CSR_STATUS
> +	csrr t2, CSR_EPC
> +	csrr t3, CSR_TVAL
> +	csrr t4, CSR_CAUSE
> +
> +	REG_S t1, PT_STATUS(a0)
> +	REG_S t2, PT_EPC(a0)
> +	REG_S t3, PT_BADADDR(a0)
> +	REG_S t4, PT_CAUSE(a0)
> +	ret
> +SYM_CODE_END(riscv_crash_save_regs)
> diff --git a/arch/riscv/kernel/kexec_relocate.S b/arch/riscv/kernel/kexec_relocate.S
> index 616c20771..14220f70f 100644
> --- a/arch/riscv/kernel/kexec_relocate.S
> +++ b/arch/riscv/kernel/kexec_relocate.S
> @@ -150,7 +150,73 @@ SYM_CODE_START(riscv_kexec_relocate)
>   SYM_CODE_END(riscv_kexec_relocate)
>   riscv_kexec_relocate_end:
>   
> -	.section ".rodata"
> +
> +/* Used for jumping to crashkernel */
> +.section ".text"
> +SYM_CODE_START(riscv_kexec_norelocate)
> +	/*
> +	 * s0: (const) Phys address to jump to
> +	 * s1: (const) Phys address of the FDT image
> +	 * s2: (const) The hartid of the current hart
> +	 * s3: (const) va_pa_offset, used when switching MMU off
> +	 */
> +	mv	s0, a1
> +	mv	s1, a2
> +	mv	s2, a3
> +	mv	s3, a4
> +
> +	/* Disable / cleanup interrupts */
> +	csrw	sie, zero
> +	csrw	sip, zero
> +
> +	/* Switch to physical addressing */
> +	la	s4, 1f
> +	sub	s4, s4, s3
> +	csrw	stvec, s4
> +	csrw	sptbr, zero

satp is used everywhere instead of sptbr. And maybe you could CSR_**** 
naming, like you did in riscv_crash_save_regs and like it's done in 
head.S too.

> +
> +.align 2
> +1:
> +	/* Pass the arguments to the next kernel  / Cleanup*/
> +	mv	a0, s2
> +	mv	a1, s1
> +	mv	a2, s0
> +
> +	/* Cleanup */
> +	mv	a3, zero
> +	mv	a4, zero
> +	mv	a5, zero
> +	mv	a6, zero
> +	mv	a7, zero
> +
> +	mv	s0, zero
> +	mv	s1, zero
> +	mv	s2, zero
> +	mv	s3, zero
> +	mv	s4, zero
> +	mv	s5, zero
> +	mv	s6, zero
> +	mv	s7, zero
> +	mv	s8, zero
> +	mv	s9, zero
> +	mv	s10, zero
> +	mv	s11, zero
> +
> +	mv	t0, zero
> +	mv	t1, zero
> +	mv	t2, zero
> +	mv	t3, zero
> +	mv	t4, zero
> +	mv	t5, zero
> +	mv	t6, zero
> +	csrw	sepc, zero
> +	csrw	scause, zero
> +	csrw	sscratch, zero
> +
> +	jalr	zero, a2, 0
> +SYM_CODE_END(riscv_kexec_norelocate)
> +
> +.section ".rodata"
>   SYM_DATA(riscv_kexec_relocate_size,
>   	.long riscv_kexec_relocate_end - riscv_kexec_relocate)
>   
> diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c
> index 2ce6c3daf..e0596c0ac 100644
> --- a/arch/riscv/kernel/machine_kexec.c
> +++ b/arch/riscv/kernel/machine_kexec.c
> @@ -59,11 +59,6 @@ machine_kexec_prepare(struct kimage *image)
>   
>   	kexec_image_info(image);
>   
> -	if (image->type == KEXEC_TYPE_CRASH) {
> -		pr_warn("Loading a crash kernel is unsupported for now.\n");
> -		return -EINVAL;
> -	}
> -
>   	/* Find the Flattened Device Tree and save its physical address */
>   	for (i = 0; i < image->nr_segments; i++) {
>   		if (image->segment[i].memsz <= sizeof(fdt))
> @@ -85,17 +80,21 @@ machine_kexec_prepare(struct kimage *image)
>   	}
>   
>   	/* Copy the assembler code for relocation to the control page */
> -	control_code_buffer = page_address(image->control_code_page);
> -	control_code_buffer_sz = page_size(image->control_code_page);
> -	if (unlikely(riscv_kexec_relocate_size > control_code_buffer_sz)) {
> -		pr_err("Relocation code doesn't fit within a control page\n");
> -		return -EINVAL;
> -	}
> -	memcpy(control_code_buffer, riscv_kexec_relocate,
> -		riscv_kexec_relocate_size);
> +	if (image->type != KEXEC_TYPE_CRASH) {
> +		control_code_buffer = page_address(image->control_code_page);
> +		control_code_buffer_sz = page_size(image->control_code_page);
>   
> -	/* Mark the control page executable */
> -	set_memory_x((unsigned long) control_code_buffer, 1);
> +		if (unlikely(riscv_kexec_relocate_size > control_code_buffer_sz)) {
> +			pr_err("Relocation code doesn't fit within a control page\n");
> +			return -EINVAL;
> +		}
> +
> +		memcpy(control_code_buffer, riscv_kexec_relocate,
> +			riscv_kexec_relocate_size);
> +
> +		/* Mark the control page executable */
> +		set_memory_x((unsigned long) control_code_buffer, 1);
> +	}
>   
>   	return 0;
>   }
> @@ -147,6 +146,9 @@ void machine_shutdown(void)
>   void
>   machine_crash_shutdown(struct pt_regs *regs)
>   {
> +	crash_save_cpu(regs, smp_processor_id());
> +	machine_shutdown();
> +	pr_info("Starting crashdump kernel...\n");
>   }
>   
>   /**
> @@ -169,7 +171,12 @@ machine_kexec(struct kimage *image)
>   	unsigned long this_hart_id = raw_smp_processor_id();
>   	unsigned long fdt_addr = internal->fdt_addr;
>   	void *control_code_buffer = page_address(image->control_code_page);
> -	riscv_kexec_do_relocate do_relocate = control_code_buffer;
> +	riscv_kexec_method kexec_method = NULL;
> +
> +	if (image->type != KEXEC_TYPE_CRASH)
> +		kexec_method = control_code_buffer;
> +	else
> +		kexec_method = (riscv_kexec_method) &riscv_kexec_norelocate;
>   
>   	pr_notice("Will call new kernel at %08lx from hart id %lx\n",
>   		  jump_addr, this_hart_id);
> @@ -180,7 +187,7 @@ machine_kexec(struct kimage *image)
>   
>   	/* Jump to the relocation code */
>   	pr_notice("Bye...\n");
> -	do_relocate(first_ind_entry, jump_addr, fdt_addr,
> -		    this_hart_id, va_pa_offset);
> +	kexec_method(first_ind_entry, jump_addr, fdt_addr,
> +		     this_hart_id, va_pa_offset);
>   	unreachable();
>   }
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 030554bab..31866dce9 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -20,6 +20,7 @@
>   #include <linux/swiotlb.h>
>   #include <linux/smp.h>
>   #include <linux/efi.h>
> +#include <linux/crash_dump.h>
>   
>   #include <asm/cpu_ops.h>
>   #include <asm/early_ioremap.h>
> @@ -160,6 +161,14 @@ static void __init init_resources(void)
>   	if (ret < 0)
>   		goto error;
>   
> +#ifdef CONFIG_KEXEC_CORE
> +	if (crashk_res.start != crashk_res.end) {
> +		ret = add_resource(&iomem_resource, &crashk_res);
> +		if (ret < 0)
> +			goto error;
> +	}
> +#endif
> +
>   	for_each_reserved_mem_region(region) {
>   		res = &mem_res[res_idx--];
>   
> @@ -252,7 +261,6 @@ void __init setup_arch(char **cmdline_p)
>   	efi_init();
>   	setup_bootmem();
>   	paging_init();
> -	init_resources();
>   #if IS_ENABLED(CONFIG_BUILTIN_DTB)
>   	unflatten_and_copy_device_tree();
>   #else
> @@ -263,6 +271,7 @@ void __init setup_arch(char **cmdline_p)
>   #endif
>   	misc_mem_init();
>   
> +	init_resources();
>   	sbi_init();
>   
>   	if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 7f5036fbe..e71b35cec 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -2,6 +2,8 @@
>   /*
>    * Copyright (C) 2012 Regents of the University of California
>    * Copyright (C) 2019 Western Digital Corporation or its affiliates.
> + * Copyright (C) 2020 FORTH-ICS/CARV
> + *  Nick Kossifidis <mick@ics.forth.gr>
>    */
>   
>   #include <linux/init.h>
> @@ -14,6 +16,7 @@
>   #include <linux/libfdt.h>
>   #include <linux/set_memory.h>
>   #include <linux/dma-map-ops.h>
> +#include <linux/crash_dump.h>
>   
>   #include <asm/fixmap.h>
>   #include <asm/tlbflush.h>
> @@ -586,6 +589,77 @@ void mark_rodata_ro(void)
>   }
>   #endif
>   
> +#ifdef CONFIG_KEXEC_CORE
> +/*
> + * reserve_crashkernel() - reserves memory for crash kernel
> + *
> + * This function reserves memory area given in "crashkernel=" kernel command
> + * line parameter. The memory reserved is used by dump capture kernel when
> + * primary kernel is crashing.
> + */
> +static void __init reserve_crashkernel(void)
> +{
> +	unsigned long long crash_base = 0;
> +	unsigned long long crash_size = 0;
> +	unsigned long search_start = memblock_start_of_DRAM();
> +	unsigned long search_end = memblock_end_of_DRAM();
> +
> +	int ret = 0;
> +
> +	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> +				&crash_size, &crash_base);
> +	if (ret || !crash_size)
> +		return;
> +
> +	crash_size = PAGE_ALIGN(crash_size);
> +
> +	if (crash_base == 0) {
> +		/*
> +		 * Current riscv boot protocol requires 2MB alignment for
> +		 * RV64 and 4MB alignment for RV32 (hugepage size)
> +		 */
> +		crash_base = memblock_find_in_range(search_start, search_end,
> +#ifdef CONFIG_64BIT
> +						    crash_size, SZ_2M);
> +#else
> +						    crash_size, SZ_4M);
> +#endif

You can use PMD_SIZE here and get rid of #ifdef.

> +		if (crash_base == 0) {
> +			pr_warn("crashkernel: couldn't allocate %lldKB\n",
> +				crash_size >> 10);
> +			return;
> +		}
> +	} else {
> +		/* User specifies base address explicitly. */
> +		if (!memblock_is_region_memory(crash_base, crash_size)) {
> +			pr_warn("crashkernel: requested region is not memory\n");
> +			return;
> +		}
> +
> +		if (memblock_is_region_reserved(crash_base, crash_size)) {
> +			pr_warn("crashkernel: requested region is reserved\n");
> +			return;
> +		}
> +
> +#ifdef CONFIG_64BIT
> +		if (!IS_ALIGNED(crash_base, SZ_2M)) {
> +#else
> +		if (!IS_ALIGNED(crash_base, SZ_4M)) {
> +#endif

Ditto here.

> +			pr_warn("crashkernel: requested region is misaligned\n");
> +			return;
> +		}
> +	}
> +	memblock_reserve(crash_base, crash_size);
> +
> +	pr_info("crashkernel: reserved 0x%016llx - 0x%016llx (%lld MB)\n",
> +		crash_base, crash_base + crash_size, crash_size >> 20);
> +
> +	crashk_res.start = crash_base;
> +	crashk_res.end = crash_base + crash_size - 1;
> +}
> +#endif /* CONFIG_KEXEC_CORE */
> +
>   void __init paging_init(void)
>   {
>   	setup_vm_final();
> @@ -598,6 +672,9 @@ void __init misc_mem_init(void)
>   	arch_numa_init();
>   	sparse_init();
>   	zone_sizes_init();
> +#ifdef CONFIG_KEXEC_CORE
> +	reserve_crashkernel();
> +#endif
>   	memblock_dump_all();
>   }
>   
>