[PATCH v3 2/5] RISC-V: Add kexec support

Nick Kossifidis
2021-04-05T08:57:58Z

This patch adds support for kexec on RISC-V. On SMP systems it depends
on HOTPLUG_CPU in order to be able to bring up all harts after kexec.
It also needs a recent OpenSBI version that supports the HSM extension.
I tested it on riscv64 QEMU on both an smp and a non-smp system.

v5:
* For now depend on MMU, further changes needed for NOMMU support
* Make sure stvec is aligned
* Cleanup some unneeded fences
* Verify control code's buffer size
* Compile kexec_relocate.S with medany and norelax

v4:
* No functional changes, just re-based

v3:
* Use the new smp_shutdown_nonboot_cpus() call.
* Move riscv_kexec_relocate to .rodata

v2:
* Pass needed parameters as arguments to riscv_kexec_relocate
instead of using global variables.
* Use kimage_arch to hold the fdt address of the included fdt.
* Use SYM_* macros on kexec_relocate.S.
* Compatibility with STRICT_KERNEL_RWX.
* Compatibility with HOTPLUG_CPU for SMP
* Small cleanups

Signed-off-by: Nick Kossifidis <mick@ics.forth.gr>
---
arch/riscv/Kconfig | 15 +++
arch/riscv/include/asm/kexec.h | 47 ++++++++
arch/riscv/kernel/Makefile | 5 +
arch/riscv/kernel/kexec_relocate.S | 156 ++++++++++++++++++++++++
arch/riscv/kernel/machine_kexec.c | 186 +++++++++++++++++++++++++++++
5 files changed, 409 insertions(+)
create mode 100644 arch/riscv/include/asm/kexec.h
create mode 100644 arch/riscv/kernel/kexec_relocate.S
create mode 100644 arch/riscv/kernel/machine_kexec.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 8ea60a0a1..3716262ef 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -389,6 +389,21 @@ config RISCV_SBI_V01
help
This config allows kernel to use SBI v0.1 APIs. This will be
deprecated in future once legacy M-mode software are no longer in use.
+
+config KEXEC
+ bool "Kexec system call"
+ select KEXEC_CORE
+ select HOTPLUG_CPU if SMP
+ depends on MMU
+ 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.
+
+
endmenu

menu "Boot options"
diff --git a/arch/riscv/include/asm/kexec.h b/arch/riscv/include/asm/kexec.h
new file mode 100644
index 000000000..efc69feb4
--- /dev/null
+++ b/arch/riscv/include/asm/kexec.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2019 FORTH-ICS/CARV
+ * Nick Kossifidis <mick@ics.forth.gr>
+ */
+
+#ifndef _RISCV_KEXEC_H
+#define _RISCV_KEXEC_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 4096
+
+#define KEXEC_ARCH KEXEC_ARCH_RISCV
+
+static inline void
+crash_setup_regs(struct pt_regs *newregs,
+ struct pt_regs *oldregs)
+{
+ /* Dummy implementation for now */
+}
+
+
+#define ARCH_HAS_KIMAGE_ARCH
+
+struct kimage_arch {
+ unsigned long fdt_addr;
+};
+
+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);
+
+#endif
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 3dc0abde9..c2594018c 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -9,6 +9,10 @@ CFLAGS_REMOVE_patch.o = $(CC_FLAGS_FTRACE)
CFLAGS_REMOVE_sbi.o = $(CC_FLAGS_FTRACE)
endif

+ifdef CONFIG_KEXEC
+AFLAGS_kexec_relocate.o := -mcmodel=medany -mno-relax
+endif
+
extra-y += head.o
extra-y += vmlinux.lds

@@ -54,6 +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_JUMP_LABEL) += jump_label.o

diff --git a/arch/riscv/kernel/kexec_relocate.S b/arch/riscv/kernel/kexec_relocate.S
new file mode 100644
index 000000000..616c20771
--- /dev/null
+++ b/arch/riscv/kernel/kexec_relocate.S
@@ -0,0 +1,156 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2019 FORTH-ICS/CARV
+ * Nick Kossifidis <mick@ics.forth.gr>
+ */
+
+#include <asm/asm.h> /* For RISCV_* and REG_* macros */
+#include <asm/page.h> /* For PAGE_SHIFT */
+#include <linux/linkage.h> /* For SYM_* macros */
+
+.section ".rodata"
+SYM_CODE_START(riscv_kexec_relocate)
+
+ /*
+ * s0: Pointer to the current entry
+ * s1: (const) Phys address to jump to after relocation
+ * s2: (const) Phys address of the FDT image
+ * s3: (const) The hartid of the current hart
+ * s4: Pointer to the destination address for the relocation
+ * s5: (const) Number of words per page
+ * s6: (const) 1, used for subtraction
+ * s7: (const) va_pa_offset, used when switching MMU off
+ * s8: (const) Physical address of the main loop
+ * s9: (debug) indirection page counter
+ * s10: (debug) entry counter
+ * s11: (debug) copied words counter
+ */
+ mv s0, a0
+ mv s1, a1
+ mv s2, a2
+ mv s3, a3
+ mv s4, zero
+ li s5, ((1 << PAGE_SHIFT) / RISCV_SZPTR)
+ li s6, 1
+ mv s7, a4
+ mv s8, zero
+ mv s9, zero
+ mv s10, zero
+ mv s11, zero
+
+ /* Disable / cleanup interrupts */
+ csrw sie, zero
+ csrw sip, zero
+
+ /*
+ * When we switch SATP.MODE to "Bare" we'll only
+ * play with physical addresses. However the first time
+ * we try to jump somewhere, the offset on the jump
+ * will be relative to pc which will still be on VA. To
+ * deal with this we set stvec to the physical address at
+ * the start of the loop below so that we jump there in
+ * any case.
+ */
+ la s8, 1f
+ sub s8, s8, s7
+ csrw stvec, s8
+
+ /* Process entries in a loop */
+.align 2
+1:
+ addi s10, s10, 1
+ REG_L t0, 0(s0) /* t0 = *image->entry */
+ addi s0, s0, RISCV_SZPTR /* image->entry++ */
+
+ /* IND_DESTINATION entry ? -> save destination address */
+ andi t1, t0, 0x1
+ beqz t1, 2f
+ andi s4, t0, ~0x1
+ j 1b
+
+2:
+ /* IND_INDIRECTION entry ? -> update next entry ptr (PA) */
+ andi t1, t0, 0x2
+ beqz t1, 2f
+ andi s0, t0, ~0x2
+ addi s9, s9, 1
+ csrw sptbr, zero
+ jalr zero, s8, 0
+
+2:
+ /* IND_DONE entry ? -> jump to done label */
+ andi t1, t0, 0x4
+ beqz t1, 2f
+ j 4f
+
+2:
+ /*
+ * IND_SOURCE entry ? -> copy page word by word to the
+ * destination address we got from IND_DESTINATION
+ */
+ andi t1, t0, 0x8
+ beqz t1, 1b /* Unknown entry type, ignore it */
+ andi t0, t0, ~0x8
+ mv t3, s5 /* i = num words per page */
+3: /* copy loop */
+ REG_L t1, (t0) /* t1 = *src_ptr */
+ REG_S t1, (s4) /* *dst_ptr = *src_ptr */
+ addi t0, t0, RISCV_SZPTR /* stc_ptr++ */
+ addi s4, s4, RISCV_SZPTR /* dst_ptr++ */
+ sub t3, t3, s6 /* i-- */
+ addi s11, s11, 1 /* c++ */
+ beqz t3, 1b /* copy done ? */
+ j 3b
+
+4:
+ /* Pass the arguments to the next kernel / Cleanup*/
+ mv a0, s3
+ mv a1, s2
+ mv a2, s1
+
+ /* 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
+
+ /*
+ * Make sure the relocated code is visible
+ * and jump to the new kernel
+ */
+ fence.i
+
+ jalr zero, a2, 0
+
+SYM_CODE_END(riscv_kexec_relocate)
+riscv_kexec_relocate_end:
+
+ .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
new file mode 100644
index 000000000..2ce6c3daf
--- /dev/null
+++ b/arch/riscv/kernel/machine_kexec.c
@@ -0,0 +1,186 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 FORTH-ICS/CARV
+ * Nick Kossifidis <mick@ics.forth.gr>
+ */
+
+#include <linux/kexec.h>
+#include <asm/kexec.h> /* For riscv_kexec_* symbol defines */
+#include <linux/smp.h> /* For smp_send_stop () */
+#include <asm/cacheflush.h> /* For local_flush_icache_all() */
+#include <asm/barrier.h> /* For smp_wmb() */
+#include <asm/page.h> /* For PAGE_MASK */
+#include <linux/libfdt.h> /* For fdt_check_header() */
+#include <asm/set_memory.h> /* For set_memory_x() */
+#include <linux/compiler.h> /* For unreachable() */
+#include <linux/cpu.h> /* For cpu_down() */
+
+/**
+ * kexec_image_info - Print received image details
+ */
+static void
+kexec_image_info(const struct kimage *image)
+{
+ unsigned long i;
+
+ pr_debug("Kexec image info:\n");
+ pr_debug("\ttype: %d\n", image->type);
+ pr_debug("\tstart: %lx\n", image->start);
+ pr_debug("\thead: %lx\n", image->head);
+ pr_debug("\tnr_segments: %lu\n", image->nr_segments);
+
+ for (i = 0; i < image->nr_segments; i++) {
+ pr_debug("\t segment[%lu]: %016lx - %016lx", i,
+ image->segment[i].mem,
+ image->segment[i].mem + image->segment[i].memsz);
+ pr_debug("\t\t0x%lx bytes, %lu pages\n",
+ (unsigned long) image->segment[i].memsz,
+ (unsigned long) image->segment[i].memsz / PAGE_SIZE);
+ }
+}
+
+/**
+ * machine_kexec_prepare - Initialize kexec
+ *
+ * This function is called from do_kexec_load, when the user has
+ * provided us with an image to be loaded. Its goal is to validate
+ * the image and prepare the control code buffer as needed.
+ * Note that kimage_alloc_init has already been called and the
+ * control buffer has already been allocated.
+ */
+int
+machine_kexec_prepare(struct kimage *image)
+{
+ struct kimage_arch *internal = &image->arch;
+ struct fdt_header fdt = {0};
+ void *control_code_buffer = NULL;
+ unsigned int control_code_buffer_sz = 0;
+ int i = 0;
+
+ 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))
+ continue;
+
+ if (copy_from_user(&fdt, image->segment[i].buf, sizeof(fdt)))
+ continue;
+
+ if (fdt_check_header(&fdt))
+ continue;
+
+ internal->fdt_addr = (unsigned long) image->segment[i].mem;
+ break;
+ }
+
+ if (!internal->fdt_addr) {
+ pr_err("Device tree not included in the provided image\n");
+ return -EINVAL;
+ }
+
+ /* 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);
+
+ /* Mark the control page executable */
+ set_memory_x((unsigned long) control_code_buffer, 1);
+
+ return 0;
+}
+
+
+/**
+ * machine_kexec_cleanup - Cleanup any leftovers from
+ * machine_kexec_prepare
+ *
+ * This function is called by kimage_free to handle any arch-specific
+ * allocations done on machine_kexec_prepare. Since we didn't do any
+ * allocations there, this is just an empty function. Note that the
+ * control buffer is freed by kimage_free.
+ */
+void
+machine_kexec_cleanup(struct kimage *image)
+{
+}
+
+
+/*
+ * machine_shutdown - Prepare for a kexec reboot
+ *
+ * This function is called by kernel_kexec just before machine_kexec
+ * below. Its goal is to prepare the rest of the system (the other
+ * harts and possibly devices etc) for a kexec reboot.
+ */
+void machine_shutdown(void)
+{
+ /*
+ * No more interrupts on this hart
+ * until we are back up.
+ */
+ local_irq_disable();
+
+#if defined(CONFIG_HOTPLUG_CPU) && (CONFIG_SMP)
+ smp_shutdown_nonboot_cpus(smp_processor_id());
+#endif
+}
+
+/**
+ * machine_crash_shutdown - Prepare to kexec after a kernel crash
+ *
+ * This function is called by crash_kexec just before machine_kexec
+ * below and its goal is similar to machine_shutdown, but in case of
+ * a kernel crash. Since we don't handle such cases yet, this function
+ * is empty.
+ */
+void
+machine_crash_shutdown(struct pt_regs *regs)
+{
+}
+
+/**
+ * machine_kexec - Jump to the loaded kimage
+ *
+ * This function is called by kernel_kexec which is called by the
+ * reboot system call when the reboot cmd is LINUX_REBOOT_CMD_KEXEC,
+ * or by crash_kernel which is called by the kernel's arch-specific
+ * trap handler in case of a kernel panic. It's the final stage of
+ * the kexec process where the pre-loaded kimage is ready to be
+ * executed. We assume at this point that all other harts are
+ * suspended and this hart will be the new boot hart.
+ */
+void __noreturn
+machine_kexec(struct kimage *image)
+{
+ struct kimage_arch *internal = &image->arch;
+ unsigned long jump_addr = (unsigned long) image->start;
+ unsigned long first_ind_entry = (unsigned long) &image->head;
+ 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;
+
+ pr_notice("Will call new kernel at %08lx from hart id %lx\n",
+ jump_addr, this_hart_id);
+ pr_notice("FDT image at %08lx\n", fdt_addr);
+
+ /* Make sure the relocation code is visible to the hart */
+ local_flush_icache_all();
+
+ /* Jump to the relocation code */
+ pr_notice("Bye...\n");
+ do_relocate(first_ind_entry, jump_addr, fdt_addr,
+ this_hart_id, va_pa_offset);
+ unreachable();
+}
--
2.26.2