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

Alex Ghiti
2021-04-06T18:39:04Z

Le 4/5/21 à 4:57 AM, Nick Kossifidis a écrit :
> 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

PAGE_SIZE instead ?

> +
> +#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

Other obj-$() use parenthesis.

>
> 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)

1 << PAGE_SHIFT = PAGE_SIZE

> + 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;
> + * harts and possibly devices etc) for a kexec reboot.
> + */
> +void machine_shutdown(void)
> +
> + 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)

Shouldn't it be defined(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();
> +}