[PATCH v3 5/5] RISC-V: Add crash kernel support

Nick Kossifidis
2021-04-05T08:57:55Z

From: Nick Kossifidis <mickflemm@gmail.com>

This patch allows Linux to act as a crash kernel for use with
kdump. Userspace will let the crash kernel know about the
memory region it can use through linux,usable-memory property
on the /memory node (overriding its reg property), and about the
memory region where the elf core header of the previous kernel
is saved, through a reserved-memory node with a compatible string
of "linux,elfcorehdr". This approach is the least invasive and
re-uses functionality already present.

I tested this on riscv64 qemu and it works as expected, you
may test it by retrieving the dmesg of the previous kernel
through /proc/vmcore, using the vmcore-dmesg utility from
kexec-tools.

v3:
* Rebase

v2:
* Use linux,usable-memory on /memory instead of a new binding
* Use a reserved-memory node for ELF core header

Signed-off-by: Nick Kossifidis <mick@ics.forth.gr>
---
arch/riscv/Kconfig | 10 ++++++++
arch/riscv/kernel/Makefile | 1 +
arch/riscv/kernel/crash_dump.c | 46 ++++++++++++++++++++++++++++++++++
arch/riscv/kernel/setup.c | 12 +++++++++
arch/riscv/mm/init.c | 33 ++++++++++++++++++++++++
5 files changed, 102 insertions(+)
create mode 100644 arch/riscv/kernel/crash_dump.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 3716262ef..553c2dced 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -403,6 +403,16 @@ config KEXEC

The name comes from the similarity to the exec system call.

+config CRASH_DUMP
+ bool "Build kdump crash kernel"
+ help
+ Generate crash dump after being started by kexec. This should
+ be normally only set in special crash dump kernels which are
+ loaded in the main kernel with kexec-tools into a specially
+ reserved region and then later executed after a crash by
+ kdump/kexec.
+
+ For more details see Documentation/admin-guide/kdump/kdump.rst

endmenu

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 07f676ad3..bd66d2ce0 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -59,6 +59,7 @@ endif
obj-$(CONFIG_HOTPLUG_CPU) += cpu-hotplug.o
obj-$(CONFIG_KGDB) += kgdb.o
obj-${CONFIG_KEXEC} += kexec_relocate.o crash_save_regs.o machine_kexec.o
+obj-$(CONFIG_CRASH_DUMP) += crash_dump.o

obj-$(CONFIG_JUMP_LABEL) += jump_label.o

diff --git a/arch/riscv/kernel/crash_dump.c b/arch/riscv/kernel/crash_dump.c
new file mode 100644
index 000000000..86cc0ada5
--- /dev/null
+++ b/arch/riscv/kernel/crash_dump.c
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This code comes from arch/arm64/kernel/crash_dump.c
+ * Created by: AKASHI Takahiro <takahiro.akashi@linaro.org>
+ * Copyright (C) 2017 Linaro Limited
+ */
+
+#include <linux/crash_dump.h>
+#include <linux/io.h>
+
+/**
+ * copy_oldmem_page() - copy one page from old kernel memory
+ * @pfn: page frame number to be copied
+ * @buf: buffer where the copied page is placed
+ * @csize: number of bytes to copy
+ * @offset: offset in bytes into the page
+ * @userbuf: if set, @buf is in a user address space
+ *
+ * This function copies one page from old kernel memory into buffer pointed by
+ * @buf. If @buf is in userspace, set @userbuf to %1. Returns number of bytes
+ * copied or negative error in case of failure.
+ */
+ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
+ size_t csize, unsigned long offset,
+ int userbuf)
+{
+ void *vaddr;
+
+ if (!csize)
+ return 0;
+
+ vaddr = memremap(__pfn_to_phys(pfn), PAGE_SIZE, MEMREMAP_WB);
+ if (!vaddr)
+ return -ENOMEM;
+
+ if (userbuf) {
+ if (copy_to_user((char __user *)buf, vaddr + offset, csize)) {
+ memunmap(vaddr);
+ return -EFAULT;
+ }
+ } else
+ memcpy(buf, vaddr + offset, csize);
+
+ memunmap(vaddr);
+ return csize;
+}
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 31866dce9..ff398a3d8 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -66,6 +66,9 @@ static struct resource code_res = { .name = "Kernel code", };
static struct resource data_res = { .name = "Kernel data", };
static struct resource rodata_res = { .name = "Kernel rodata", };
static struct resource bss_res = { .name = "Kernel bss", };
+#ifdef CONFIG_CRASH_DUMP
+static struct resource elfcorehdr_res = { .name = "ELF Core hdr", };
+#endif

static int __init add_resource(struct resource *parent,
struct resource *res)
@@ -169,6 +172,15 @@ static void __init init_resources(void)
}
#endif

+#ifdef CONFIG_CRASH_DUMP
+ if (elfcorehdr_size > 0) {
+ elfcorehdr_res.start = elfcorehdr_addr;
+ elfcorehdr_res.end = elfcorehdr_addr + elfcorehdr_size - 1;
+ elfcorehdr_res.flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
+ add_resource(&iomem_resource, &elfcorehdr_res);
+ }
+#endif
+
for_each_reserved_mem_region(region) {
res = &mem_res[res_idx--];

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index e71b35cec..f66011816 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -13,6 +13,7 @@
#include <linux/swap.h>
#include <linux/sizes.h>
#include <linux/of_fdt.h>
+#include <linux/of_reserved_mem.h>
#include <linux/libfdt.h>
#include <linux/set_memory.h>
#include <linux/dma-map-ops.h>
@@ -606,6 +607,18 @@ static void __init reserve_crashkernel(void)

int ret = 0;

+ /*
+ * Don't reserve a region for a crash kernel on a crash kernel
+ * since it doesn't make much sense and we have limited memory
+ * resources.
+ */
+#ifdef CONFIG_CRASH_DUMP
+ if (is_kdump_kernel()) {
+ pr_info("crashkernel: ignoring reservation request\n");
+ return;
+ }
+#endif
+
ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
&crash_size, &crash_base);
if (ret || !crash_size)
@@ -660,6 +673,26 @@ static void __init reserve_crashkernel(void)
}
#endif /* CONFIG_KEXEC_CORE */

+#ifdef CONFIG_CRASH_DUMP
+/*
+ * We keep track of the ELF core header of the crashed
+ * kernel with a reserved-memory region with compatible
+ * string "linux,elfcorehdr". Here we register a callback
+ * to populate elfcorehdr_addr/size when this region is
+ * present. Note that this region will be marked as
+ * reserved once we call early_init_fdt_scan_reserved_mem()
+ * later on.
+ */
+static int elfcore_hdr_setup(struct reserved_mem *rmem)
+{
+ elfcorehdr_addr = rmem->base;
+ elfcorehdr_size = rmem->size;
+ return 0;
+}
+
+RESERVEDMEM_OF_DECLARE(elfcorehdr, "linux,elfcorehdr", elfcore_hdr_setup);
+#endif
+
void __init paging_init(void)
{
setup_vm_final();
--
2.26.2