RISC-V: Add crash kernel support

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.

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

1 files changed, 33 insertions, 0 deletions

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 63c94d33e18a..3cb4c1b6cee1 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>
@@ -678,6 +679,18 @@ 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)
@@ -726,6 +739,26 @@ 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();