[PATCH v4 10/10] ARM: Parse kdump DT properties
From: Geert Uytterhoeven
Date: Wed Jul 14 2021 - 08:51:57 EST
Parse the following DT properties in the crash dump kernel, to provide a
modern interface between kexec and the crash dump kernel:
- linux,elfcorehdr: ELF core header segment, similar to the
"elfcorehdr=" kernel parameter.
- linux,usable-memory-range: Usable memory reserved for the crash dump
kernel.
This makes the memory reservation explicit. If present, Linux no
longer needs to mask the program counter, and rely on the "mem="
kernel parameter to obtain the start and size of usable memory.
For backwards compatibility, the traditional method to derive the start
of memory is still used if "linux,usable-memory-range" is absent, and
the "elfcorehdr=" and "mem=" kernel parameters are still parsed.
Loosely based on the ARM64 version by Akashi Takahiro.
Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
---
The corresponding patch for kexec-tools is "[PATCH] arm: kdump: Add DT
properties to crash dump kernel's DTB", which is still valid:
https://lore.kernel.org/linux-arm-kernel/20200902154129.6358-1-geert+renesas@xxxxxxxxx/
v4:
- Remove references to architectures in chosen.txt, to avoid having to
change this again when more architectures copy kdump support,
- Remove the architecture-specific code for parsing
"linux,usable-memory-range" and "linux,elfcorehdr", as the FDT core
code now takes care of this,
- Move chosen.txt change to patch changing the FDT core,
- Use IS_ENABLED(CONFIG_CRASH_DUMP) instead of #ifdef,
v3:
- Rebase on top of accepted solution for DTB memory information
handling, which is part of v5.12-rc1,
v2:
- Rebase on top of reworked DTB memory information handling.
---
.../arm/boot/compressed/fdt_check_mem_start.c | 48 ++++++++++++++++---
arch/arm/mm/init.c | 30 ++++++++++++
2 files changed, 72 insertions(+), 6 deletions(-)
diff --git a/arch/arm/boot/compressed/fdt_check_mem_start.c b/arch/arm/boot/compressed/fdt_check_mem_start.c
index 62450d824c3ca180..9291a2661bdfe57f 100644
--- a/arch/arm/boot/compressed/fdt_check_mem_start.c
+++ b/arch/arm/boot/compressed/fdt_check_mem_start.c
@@ -55,16 +55,17 @@ static uint64_t get_val(const fdt32_t *cells, uint32_t ncells)
* DTB, and, if out-of-range, replace it by the real start address.
* To preserve backwards compatibility (systems reserving a block of memory
* at the start of physical memory, kdump, ...), the traditional method is
- * always used if it yields a valid address.
+ * used if it yields a valid address, unless the "linux,usable-memory-range"
+ * property is present.
*
* Return value: start address of physical memory to use
*/
uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
{
- uint32_t addr_cells, size_cells, base;
+ uint32_t addr_cells, size_cells, usable_base, base;
uint32_t fdt_mem_start = 0xffffffff;
- const fdt32_t *reg, *endp;
- uint64_t size, end;
+ const fdt32_t *usable, *reg, *endp;
+ uint64_t size, usable_end, end;
const char *type;
int offset, len;
@@ -80,6 +81,27 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
if (addr_cells > 2 || size_cells > 2)
return mem_start;
+ /*
+ * Usable memory in case of a crash dump kernel
+ * This property describes a limitation: memory within this range is
+ * only valid when also described through another mechanism
+ */
+ usable = get_prop(fdt, "/chosen", "linux,usable-memory-range",
+ (addr_cells + size_cells) * sizeof(fdt32_t));
+ if (usable) {
+ size = get_val(usable + addr_cells, size_cells);
+ if (!size)
+ return mem_start;
+
+ if (addr_cells > 1 && fdt32_ld(usable)) {
+ /* Outside 32-bit address space */
+ return mem_start;
+ }
+
+ usable_base = fdt32_ld(usable + addr_cells - 1);
+ usable_end = usable_base + size;
+ }
+
/* Walk all memory nodes and regions */
for (offset = fdt_next_node(fdt, -1, NULL); offset >= 0;
offset = fdt_next_node(fdt, offset, NULL)) {
@@ -107,7 +129,20 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
base = fdt32_ld(reg + addr_cells - 1);
end = base + size;
- if (mem_start >= base && mem_start < end) {
+ if (usable) {
+ /*
+ * Clip to usable range, which takes precedence
+ * over mem_start
+ */
+ if (base < usable_base)
+ base = usable_base;
+
+ if (end > usable_end)
+ end = usable_end;
+
+ if (end <= base)
+ continue;
+ } else if (mem_start >= base && mem_start < end) {
/* Calculated address is valid, use it */
return mem_start;
}
@@ -123,7 +158,8 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
}
/*
- * The calculated address is not usable.
+ * The calculated address is not usable, or was overridden by the
+ * "linux,usable-memory-range" property.
* Use the lowest usable physical memory address from the DTB instead,
* and make sure this is a multiple of 2 MiB for phys/virt patching.
*/
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 6162a070a4104a26..dfaee199554dda97 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -4,6 +4,7 @@
*
* Copyright (C) 1995-2005 Russell King
*/
+#include <linux/crash_dump.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/swap.h>
@@ -221,8 +222,35 @@ void check_cpu_icache_size(int cpuid)
}
#endif
+/*
+ * reserve_elfcorehdr() - reserves memory for elf core header
+ *
+ * This function reserves the memory occupied by an elf core header
+ * described in the device tree. This region contains all the
+ * information about primary kernel's core image and is used by a dump
+ * capture kernel to access the system memory on primary kernel.
+ */
+static void __init reserve_elfcorehdr(void)
+{
+ if (!IS_ENABLED(CONFIG_CRASH_DUMP) || !elfcorehdr_size)
+ return;
+
+ if (memblock_is_region_reserved(elfcorehdr_addr, elfcorehdr_size)) {
+ pr_warn("elfcorehdr is overlapped\n");
+ return;
+ }
+
+ memblock_reserve(elfcorehdr_addr, elfcorehdr_size);
+
+ pr_info("Reserving %llu KiB of memory at 0x%llx for elfcorehdr\n",
+ elfcorehdr_size >> 10, elfcorehdr_addr);
+}
+
void __init arm_memblock_init(const struct machine_desc *mdesc)
{
+ /* Handle linux,usable-memory-range property */
+ memblock_cap_memory_range(cap_mem_addr, cap_mem_size);
+
/* Register the kernel text, kernel data and initrd with memblock. */
memblock_reserve(__pa(KERNEL_START), KERNEL_END - KERNEL_START);
@@ -236,6 +264,8 @@ void __init arm_memblock_init(const struct machine_desc *mdesc)
early_init_fdt_scan_reserved_mem();
+ reserve_elfcorehdr();
+
/* reserve memory for DMA contiguous allocations */
dma_contiguous_reserve(arm_dma_limit);
--
2.25.1