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RISC-V: Add kexec support
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. Signed-off-by: Nick Kossifidis <[email protected]> Signed-off-by: Palmer Dabbelt <[email protected]>
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‎arch/riscv/Kconfig‎

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@@ -391,6 +391,21 @@ config RISCV_SBI_V01
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help
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This config allows kernel to use SBI v0.1 APIs. This will be
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deprecated in future once legacy M-mode software are no longer in use.
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config KEXEC
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bool "Kexec system call"
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select KEXEC_CORE
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select HOTPLUG_CPU if SMP
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depends on MMU
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help
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kexec is a system call that implements the ability to shutdown your
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current kernel, and to start another kernel. It is like a reboot
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but it is independent of the system firmware. And like a reboot
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you can start any kernel with it, not just Linux.
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The name comes from the similarity to the exec system call.
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endmenu
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menu "Boot options"

‎arch/riscv/include/asm/kexec.h‎

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/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 2019 FORTH-ICS/CARV
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* Nick Kossifidis <[email protected]>
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*/
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#ifndef _RISCV_KEXEC_H
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#define _RISCV_KEXEC_H
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#include <asm/page.h> /* For PAGE_SIZE */
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/* Maximum physical address we can use pages from */
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#define KEXEC_SOURCE_MEMORY_LIMIT (-1UL)
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/* Maximum address we can reach in physical address mode */
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#define KEXEC_DESTINATION_MEMORY_LIMIT (-1UL)
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/* Maximum address we can use for the control code buffer */
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#define KEXEC_CONTROL_MEMORY_LIMIT (-1UL)
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/* Reserve a page for the control code buffer */
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#define KEXEC_CONTROL_PAGE_SIZE PAGE_SIZE
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#define KEXEC_ARCH KEXEC_ARCH_RISCV
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static inline void
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crash_setup_regs(struct pt_regs *newregs,
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struct pt_regs *oldregs)
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{
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/* Dummy implementation for now */
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}
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#define ARCH_HAS_KIMAGE_ARCH
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struct kimage_arch {
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unsigned long fdt_addr;
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};
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const extern unsigned char riscv_kexec_relocate[];
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const extern unsigned int riscv_kexec_relocate_size;
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typedef void (*riscv_kexec_do_relocate)(unsigned long first_ind_entry,
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unsigned long jump_addr,
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unsigned long fdt_addr,
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unsigned long hartid,
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unsigned long va_pa_off);
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#endif

‎arch/riscv/kernel/Makefile‎

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@@ -9,6 +9,10 @@ CFLAGS_REMOVE_patch.o = $(CC_FLAGS_FTRACE)
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CFLAGS_REMOVE_sbi.o = $(CC_FLAGS_FTRACE)
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endif
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ifdef CONFIG_KEXEC
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AFLAGS_kexec_relocate.o := -mcmodel=medany -mno-relax
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endif
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extra-y += head.o
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extra-y += vmlinux.lds
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@@ -54,6 +58,7 @@ obj-$(CONFIG_SMP) += cpu_ops_sbi.o
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endif
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obj-$(CONFIG_HOTPLUG_CPU) += cpu-hotplug.o
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obj-$(CONFIG_KGDB) += kgdb.o
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obj-$(CONFIG_KEXEC) += kexec_relocate.o machine_kexec.o
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obj-$(CONFIG_JUMP_LABEL) += jump_label.o
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‎arch/riscv/kernel/kexec_relocate.S‎

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/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 2019 FORTH-ICS/CARV
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* Nick Kossifidis <[email protected]>
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*/
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#include <asm/asm.h> /* For RISCV_* and REG_* macros */
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#include <asm/csr.h> /* For CSR_* macros */
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#include <asm/page.h> /* For PAGE_SIZE */
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#include <linux/linkage.h> /* For SYM_* macros */
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.section ".rodata"
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SYM_CODE_START(riscv_kexec_relocate)
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/*
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* s0: Pointer to the current entry
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* s1: (const) Phys address to jump to after relocation
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* s2: (const) Phys address of the FDT image
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* s3: (const) The hartid of the current hart
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* s4: Pointer to the destination address for the relocation
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* s5: (const) Number of words per page
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* s6: (const) 1, used for subtraction
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* s7: (const) va_pa_offset, used when switching MMU off
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* s8: (const) Physical address of the main loop
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* s9: (debug) indirection page counter
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* s10: (debug) entry counter
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* s11: (debug) copied words counter
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*/
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mv s0, a0
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mv s1, a1
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mv s2, a2
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mv s3, a3
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mv s4, zero
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li s5, (PAGE_SIZE / RISCV_SZPTR)
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li s6, 1
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mv s7, a4
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mv s8, zero
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mv s9, zero
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mv s10, zero
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mv s11, zero
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/* Disable / cleanup interrupts */
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csrw CSR_SIE, zero
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csrw CSR_SIP, zero
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/*
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* When we switch SATP.MODE to "Bare" we'll only
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* play with physical addresses. However the first time
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* we try to jump somewhere, the offset on the jump
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* will be relative to pc which will still be on VA. To
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* deal with this we set stvec to the physical address at
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* the start of the loop below so that we jump there in
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* any case.
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*/
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la s8, 1f
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sub s8, s8, s7
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csrw CSR_STVEC, s8
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/* Process entries in a loop */
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.align 2
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1:
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addi s10, s10, 1
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REG_L t0, 0(s0) /* t0 = *image->entry */
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addi s0, s0, RISCV_SZPTR /* image->entry++ */
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/* IND_DESTINATION entry ? -> save destination address */
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andi t1, t0, 0x1
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beqz t1, 2f
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andi s4, t0, ~0x1
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j 1b
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2:
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/* IND_INDIRECTION entry ? -> update next entry ptr (PA) */
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andi t1, t0, 0x2
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beqz t1, 2f
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andi s0, t0, ~0x2
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addi s9, s9, 1
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csrw CSR_SATP, zero
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jalr zero, s8, 0
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2:
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/* IND_DONE entry ? -> jump to done label */
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andi t1, t0, 0x4
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beqz t1, 2f
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j 4f
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2:
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/*
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* IND_SOURCE entry ? -> copy page word by word to the
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* destination address we got from IND_DESTINATION
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*/
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andi t1, t0, 0x8
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beqz t1, 1b /* Unknown entry type, ignore it */
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andi t0, t0, ~0x8
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mv t3, s5 /* i = num words per page */
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3: /* copy loop */
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REG_L t1, (t0) /* t1 = *src_ptr */
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REG_S t1, (s4) /* *dst_ptr = *src_ptr */
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addi t0, t0, RISCV_SZPTR /* stc_ptr++ */
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addi s4, s4, RISCV_SZPTR /* dst_ptr++ */
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sub t3, t3, s6 /* i-- */
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addi s11, s11, 1 /* c++ */
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beqz t3, 1b /* copy done ? */
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j 3b
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4:
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/* Pass the arguments to the next kernel / Cleanup*/
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mv a0, s3
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mv a1, s2
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mv a2, s1
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/* Cleanup */
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mv a3, zero
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mv a4, zero
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mv a5, zero
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mv a6, zero
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mv a7, zero
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mv s0, zero
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mv s1, zero
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mv s2, zero
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mv s3, zero
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mv s4, zero
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mv s5, zero
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mv s6, zero
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mv s7, zero
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mv s8, zero
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mv s9, zero
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mv s10, zero
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mv s11, zero
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mv t0, zero
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mv t1, zero
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mv t2, zero
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mv t3, zero
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mv t4, zero
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mv t5, zero
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mv t6, zero
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csrw CSR_SEPC, zero
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csrw CSR_SCAUSE, zero
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csrw CSR_SSCRATCH, zero
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/*
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* Make sure the relocated code is visible
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* and jump to the new kernel
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*/
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fence.i
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jalr zero, a2, 0
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SYM_CODE_END(riscv_kexec_relocate)
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riscv_kexec_relocate_end:
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.section ".rodata"
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SYM_DATA(riscv_kexec_relocate_size,
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.long riscv_kexec_relocate_end - riscv_kexec_relocate)
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