RISC-V: Add kdump support

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

Signed-off-by: Nick Kossifidis <mick@ics.forth.gr>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

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 */

arch/riscv/include/asm/kexec.h

@@ -23,11 +23,16 @@
 
 #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);
 }
 
 
@@ -40,10 +45,12 @@ 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

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
 

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)

arch/riscv/kernel/kexec_relocate.S

@@ -151,7 +151,73 @@ 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	CSR_SIE, zero
+	csrw	CSR_SIP, zero
+
+	/* Switch to physical addressing */
+	la	s4, 1f
+	sub	s4, s4, s3
+	csrw	CSR_STVEC, s4
+	csrw	CSR_SATP, zero
+
+.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	CSR_SEPC, zero
+	csrw	CSR_SCAUSE, zero
+	csrw	CSR_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)
 

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();
 }

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)) {