[PATCH v3] ARM: Parse kdump DT properties

[PATCH v3] ARM: Parse kdump DT properties

[Geert Uytterhoeven]

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@glider.be>
---
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@glider.be/

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,
---
 Documentation/devicetree/bindings/chosen.txt  |  4 +-
 .../arm/boot/compressed/fdt_check_mem_start.c | 48 ++++++++--
 arch/arm/mm/init.c                            | 90 +++++++++++++++++++
 3 files changed, 134 insertions(+), 8 deletions(-)

diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
index 45e79172a646c537..ba75c58413667760 100644
--- a/Documentation/devicetree/bindings/chosen.txt
+++ b/Documentation/devicetree/bindings/chosen.txt
@@ -79,7 +79,7 @@ a different secondary CPU release mechanism)
 linux,usable-memory-range
 -------------------------
 
-This property (arm64 only) holds a base address and size, describing a
+This property (arm and arm64 only) holds a base address and size, describing a
 limited region in which memory may be considered available for use by
 the kernel. Memory outside of this range is not available for use.
 
@@ -106,7 +106,7 @@ respectively, of the root node.
 linux,elfcorehdr
 ----------------
 
-This property (currently used only on arm64) holds the memory range,
+This property (currently used only on arm and arm64) holds the memory range,
 the address and the size, of the elf core header which mainly describes
 the panicked kernel's memory layout as PT_LOAD segments of elf format.
 e.g.
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 828a2561b2295813..d1ae15d9b29121e6 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>
@@ -210,8 +211,95 @@ void check_cpu_icache_size(int cpuid)
 }
 #endif
 
+#ifdef CONFIG_OF_EARLY_FLATTREE
+static int __init early_init_dt_scan_usablemem(unsigned long node,
+		const char *uname, int depth, void *data)
+{
+	struct memblock_region *usablemem = data;
+	const __be32 *reg;
+	int len;
+
+	if (depth != 1 || strcmp(uname, "chosen") != 0)
+		return 0;
+
+	reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
+	if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
+		return 1;
+
+	usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
+	usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
+	return 1;
+}
+
+static void __init fdt_enforce_memory_region(void)
+{
+	struct memblock_region reg = {
+		.size = 0,
+	};
+
+	of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
+
+	if (reg.size)
+		memblock_cap_memory_range(reg.base, reg.size);
+}
+
+#else
+static inline void fdt_enforce_memory_region(void) { }
+#endif
+
+#if defined(CONFIG_CRASH_DUMP) && defined(CONFIG_OF_EARLY_FLATTREE)
+static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
+		const char *uname, int depth, void *data)
+{
+	const __be32 *reg;
+	int len;
+
+	if (depth != 1 || strcmp(uname, "chosen") != 0)
+		return 0;
+
+	reg = of_get_flat_dt_prop(node, "linux,elfcorehdr", &len);
+	if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
+		return 1;
+
+	elfcorehdr_addr = dt_mem_next_cell(dt_root_addr_cells, &reg);
+	elfcorehdr_size = dt_mem_next_cell(dt_root_size_cells, &reg);
+	return 1;
+}
+
+/*
+ * 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)
+{
+	of_scan_flat_dt(early_init_dt_scan_elfcorehdr, NULL);
+
+	if (!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);
+}
+#else
+static inline void reserve_elfcorehdr(void) { }
+#endif
+
 void __init arm_memblock_init(const struct machine_desc *mdesc)
 {
+	/* Handle linux,usable-memory-range property */
+	fdt_enforce_memory_region();
+
 	/* Register the kernel text, kernel data and initrd with memblock. */
 	memblock_reserve(__pa(KERNEL_START), KERNEL_END - KERNEL_START);
 
@@ -225,6 +313,8 @@ 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

[PATCH v3] ARM: Parse kdump DT properties

[Geert Uytterhoeven]

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@glider.be>
---
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@glider.be/

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,
---
 Documentation/devicetree/bindings/chosen.txt  |  4 +-
 .../arm/boot/compressed/fdt_check_mem_start.c | 48 ++++++++--
 arch/arm/mm/init.c                            | 90 +++++++++++++++++++
 3 files changed, 134 insertions(+), 8 deletions(-)

diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
index 45e79172a646c537..ba75c58413667760 100644
--- a/Documentation/devicetree/bindings/chosen.txt
+++ b/Documentation/devicetree/bindings/chosen.txt
@@ -79,7 +79,7 @@ a different secondary CPU release mechanism)
 linux,usable-memory-range
 -------------------------
 
-This property (arm64 only) holds a base address and size, describing a
+This property (arm and arm64 only) holds a base address and size, describing a
 limited region in which memory may be considered available for use by
 the kernel. Memory outside of this range is not available for use.
 
@@ -106,7 +106,7 @@ respectively, of the root node.
 linux,elfcorehdr
 ----------------
 
-This property (currently used only on arm64) holds the memory range,
+This property (currently used only on arm and arm64) holds the memory range,
 the address and the size, of the elf core header which mainly describes
 the panicked kernel's memory layout as PT_LOAD segments of elf format.
 e.g.
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 828a2561b2295813..d1ae15d9b29121e6 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>
@@ -210,8 +211,95 @@ void check_cpu_icache_size(int cpuid)
 }
 #endif
 
+#ifdef CONFIG_OF_EARLY_FLATTREE
+static int __init early_init_dt_scan_usablemem(unsigned long node,
+		const char *uname, int depth, void *data)
+{
+	struct memblock_region *usablemem = data;
+	const __be32 *reg;
+	int len;
+
+	if (depth != 1 || strcmp(uname, "chosen") != 0)
+		return 0;
+
+	reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
+	if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
+		return 1;
+
+	usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
+	usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
+	return 1;
+}
+
+static void __init fdt_enforce_memory_region(void)
+{
+	struct memblock_region reg = {
+		.size = 0,
+	};
+
+	of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
+
+	if (reg.size)
+		memblock_cap_memory_range(reg.base, reg.size);
+}
+
+#else
+static inline void fdt_enforce_memory_region(void) { }
+#endif
+
+#if defined(CONFIG_CRASH_DUMP) && defined(CONFIG_OF_EARLY_FLATTREE)
+static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
+		const char *uname, int depth, void *data)
+{
+	const __be32 *reg;
+	int len;
+
+	if (depth != 1 || strcmp(uname, "chosen") != 0)
+		return 0;
+
+	reg = of_get_flat_dt_prop(node, "linux,elfcorehdr", &len);
+	if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
+		return 1;
+
+	elfcorehdr_addr = dt_mem_next_cell(dt_root_addr_cells, &reg);
+	elfcorehdr_size = dt_mem_next_cell(dt_root_size_cells, &reg);
+	return 1;
+}
+
+/*
+ * 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)
+{
+	of_scan_flat_dt(early_init_dt_scan_elfcorehdr, NULL);
+
+	if (!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);
+}
+#else
+static inline void reserve_elfcorehdr(void) { }
+#endif
+
 void __init arm_memblock_init(const struct machine_desc *mdesc)
 {
+	/* Handle linux,usable-memory-range property */
+	fdt_enforce_memory_region();
+
 	/* Register the kernel text, kernel data and initrd with memblock. */
 	memblock_reserve(__pa(KERNEL_START), KERNEL_END - KERNEL_START);
 
@@ -225,6 +313,8 @@ 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


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[PATCH v3] ARM: Parse kdump DT properties

[Geert Uytterhoeven]

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@glider.be>
---
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@glider.be/

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,
---
 Documentation/devicetree/bindings/chosen.txt  |  4 +-
 .../arm/boot/compressed/fdt_check_mem_start.c | 48 ++++++++--
 arch/arm/mm/init.c                            | 90 +++++++++++++++++++
 3 files changed, 134 insertions(+), 8 deletions(-)

diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
index 45e79172a646c537..ba75c58413667760 100644
--- a/Documentation/devicetree/bindings/chosen.txt
+++ b/Documentation/devicetree/bindings/chosen.txt
@@ -79,7 +79,7 @@ a different secondary CPU release mechanism)
 linux,usable-memory-range
 -------------------------
 
-This property (arm64 only) holds a base address and size, describing a
+This property (arm and arm64 only) holds a base address and size, describing a
 limited region in which memory may be considered available for use by
 the kernel. Memory outside of this range is not available for use.
 
@@ -106,7 +106,7 @@ respectively, of the root node.
 linux,elfcorehdr
 ----------------
 
-This property (currently used only on arm64) holds the memory range,
+This property (currently used only on arm and arm64) holds the memory range,
 the address and the size, of the elf core header which mainly describes
 the panicked kernel's memory layout as PT_LOAD segments of elf format.
 e.g.
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 828a2561b2295813..d1ae15d9b29121e6 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>
@@ -210,8 +211,95 @@ void check_cpu_icache_size(int cpuid)
 }
 #endif
 
+#ifdef CONFIG_OF_EARLY_FLATTREE
+static int __init early_init_dt_scan_usablemem(unsigned long node,
+		const char *uname, int depth, void *data)
+{
+	struct memblock_region *usablemem = data;
+	const __be32 *reg;
+	int len;
+
+	if (depth != 1 || strcmp(uname, "chosen") != 0)
+		return 0;
+
+	reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
+	if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
+		return 1;
+
+	usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
+	usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
+	return 1;
+}
+
+static void __init fdt_enforce_memory_region(void)
+{
+	struct memblock_region reg = {
+		.size = 0,
+	};
+
+	of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
+
+	if (reg.size)
+		memblock_cap_memory_range(reg.base, reg.size);
+}
+
+#else
+static inline void fdt_enforce_memory_region(void) { }
+#endif
+
+#if defined(CONFIG_CRASH_DUMP) && defined(CONFIG_OF_EARLY_FLATTREE)
+static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
+		const char *uname, int depth, void *data)
+{
+	const __be32 *reg;
+	int len;
+
+	if (depth != 1 || strcmp(uname, "chosen") != 0)
+		return 0;
+
+	reg = of_get_flat_dt_prop(node, "linux,elfcorehdr", &len);
+	if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
+		return 1;
+
+	elfcorehdr_addr = dt_mem_next_cell(dt_root_addr_cells, &reg);
+	elfcorehdr_size = dt_mem_next_cell(dt_root_size_cells, &reg);
+	return 1;
+}
+
+/*
+ * 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)
+{
+	of_scan_flat_dt(early_init_dt_scan_elfcorehdr, NULL);
+
+	if (!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);
+}
+#else
+static inline void reserve_elfcorehdr(void) { }
+#endif
+
 void __init arm_memblock_init(const struct machine_desc *mdesc)
 {
+	/* Handle linux,usable-memory-range property */
+	fdt_enforce_memory_region();
+
 	/* Register the kernel text, kernel data and initrd with memblock. */
 	memblock_reserve(__pa(KERNEL_START), KERNEL_END - KERNEL_START);
 
@@ -225,6 +313,8 @@ 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


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH v3] ARM: Parse kdump DT properties

[Rob Herring]

On Wed, Mar 17, 2021 at 5:31 AM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
>
> 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@glider.be>
> ---
> 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@glider.be/
>
> 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,
> ---
>  Documentation/devicetree/bindings/chosen.txt  |  4 +-

Note that I've been meaning to remove this file because dtschema has a
schema replacing it.

>  .../arm/boot/compressed/fdt_check_mem_start.c | 48 ++++++++--
>  arch/arm/mm/init.c                            | 90 +++++++++++++++++++
>  3 files changed, 134 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
> index 45e79172a646c537..ba75c58413667760 100644
> --- a/Documentation/devicetree/bindings/chosen.txt
> +++ b/Documentation/devicetree/bindings/chosen.txt
> @@ -79,7 +79,7 @@ a different secondary CPU release mechanism)
>  linux,usable-memory-range
>  -------------------------
>
> -This property (arm64 only) holds a base address and size, describing a
> +This property (arm and arm64 only) holds a base address and size, describing a

I'd rather not have to change this again when RiscV gets around to
copying kdump support.

>  limited region in which memory may be considered available for use by
>  the kernel. Memory outside of this range is not available for use.
>
> @@ -106,7 +106,7 @@ respectively, of the root node.
>  linux,elfcorehdr
>  ----------------
>
> -This property (currently used only on arm64) holds the memory range,
> +This property (currently used only on arm and arm64) holds the memory range,
>  the address and the size, of the elf core header which mainly describes
>  the panicked kernel's memory layout as PT_LOAD segments of elf format.
>  e.g.
> 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 828a2561b2295813..d1ae15d9b29121e6 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>
> @@ -210,8 +211,95 @@ void check_cpu_icache_size(int cpuid)
>  }
>  #endif
>
> +#ifdef CONFIG_OF_EARLY_FLATTREE
> +static int __init early_init_dt_scan_usablemem(unsigned long node,
> +               const char *uname, int depth, void *data)
> +{
> +       struct memblock_region *usablemem = data;
> +       const __be32 *reg;
> +       int len;
> +
> +       if (depth != 1 || strcmp(uname, "chosen") != 0)
> +               return 0;

We have libfdt now, just get the '/chosen' node rather than using
of_scan_flat_dt().


> +
> +       reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
> +       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> +               return 1;
> +
> +       usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
> +       usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
> +       return 1;
> +}
> +
> +static void __init fdt_enforce_memory_region(void)
> +{
> +       struct memblock_region reg = {
> +               .size = 0,
> +       };
> +
> +       of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
> +
> +       if (reg.size)
> +               memblock_cap_memory_range(reg.base, reg.size);

We should be able to do this in the DT core code. It doesn't matter
that these properties are arm* only. Other arches won't find the
properties.

Also, note that there is now a drivers/of/kexec.c (in -next) though
not sure if all this would go there or stay in fdt.c with the rest of
the memory parsing.

> +}
> +
> +#else
> +static inline void fdt_enforce_memory_region(void) { }
> +#endif
> +
> +#if defined(CONFIG_CRASH_DUMP) && defined(CONFIG_OF_EARLY_FLATTREE)
> +static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
> +               const char *uname, int depth, void *data)

Same comments as above.

> +{
> +       const __be32 *reg;
> +       int len;
> +
> +       if (depth != 1 || strcmp(uname, "chosen") != 0)
> +               return 0;
> +
> +       reg = of_get_flat_dt_prop(node, "linux,elfcorehdr", &len);
> +       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> +               return 1;
> +
> +       elfcorehdr_addr = dt_mem_next_cell(dt_root_addr_cells, &reg);
> +       elfcorehdr_size = dt_mem_next_cell(dt_root_size_cells, &reg);
> +       return 1;
> +}
> +
> +/*
> + * 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)
> +{
> +       of_scan_flat_dt(early_init_dt_scan_elfcorehdr, NULL);
> +
> +       if (!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);
> +}
> +#else
> +static inline void reserve_elfcorehdr(void) { }
> +#endif
> +
>  void __init arm_memblock_init(const struct machine_desc *mdesc)
>  {
> +       /* Handle linux,usable-memory-range property */
> +       fdt_enforce_memory_region();
> +
>         /* Register the kernel text, kernel data and initrd with memblock. */
>         memblock_reserve(__pa(KERNEL_START), KERNEL_END - KERNEL_START);
>
> @@ -225,6 +313,8 @@ 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
>

Re: [PATCH v3] ARM: Parse kdump DT properties

[Rob Herring]

On Wed, Mar 17, 2021 at 5:31 AM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
>
> 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@glider.be>
> ---
> 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@glider.be/
>
> 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,
> ---
>  Documentation/devicetree/bindings/chosen.txt  |  4 +-

Note that I've been meaning to remove this file because dtschema has a
schema replacing it.

>  .../arm/boot/compressed/fdt_check_mem_start.c | 48 ++++++++--
>  arch/arm/mm/init.c                            | 90 +++++++++++++++++++
>  3 files changed, 134 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
> index 45e79172a646c537..ba75c58413667760 100644
> --- a/Documentation/devicetree/bindings/chosen.txt
> +++ b/Documentation/devicetree/bindings/chosen.txt
> @@ -79,7 +79,7 @@ a different secondary CPU release mechanism)
>  linux,usable-memory-range
>  -------------------------
>
> -This property (arm64 only) holds a base address and size, describing a
> +This property (arm and arm64 only) holds a base address and size, describing a

I'd rather not have to change this again when RiscV gets around to
copying kdump support.

>  limited region in which memory may be considered available for use by
>  the kernel. Memory outside of this range is not available for use.
>
> @@ -106,7 +106,7 @@ respectively, of the root node.
>  linux,elfcorehdr
>  ----------------
>
> -This property (currently used only on arm64) holds the memory range,
> +This property (currently used only on arm and arm64) holds the memory range,
>  the address and the size, of the elf core header which mainly describes
>  the panicked kernel's memory layout as PT_LOAD segments of elf format.
>  e.g.
> 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 828a2561b2295813..d1ae15d9b29121e6 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>
> @@ -210,8 +211,95 @@ void check_cpu_icache_size(int cpuid)
>  }
>  #endif
>
> +#ifdef CONFIG_OF_EARLY_FLATTREE
> +static int __init early_init_dt_scan_usablemem(unsigned long node,
> +               const char *uname, int depth, void *data)
> +{
> +       struct memblock_region *usablemem = data;
> +       const __be32 *reg;
> +       int len;
> +
> +       if (depth != 1 || strcmp(uname, "chosen") != 0)
> +               return 0;

We have libfdt now, just get the '/chosen' node rather than using
of_scan_flat_dt().


> +
> +       reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
> +       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> +               return 1;
> +
> +       usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
> +       usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
> +       return 1;
> +}
> +
> +static void __init fdt_enforce_memory_region(void)
> +{
> +       struct memblock_region reg = {
> +               .size = 0,
> +       };
> +
> +       of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
> +
> +       if (reg.size)
> +               memblock_cap_memory_range(reg.base, reg.size);

We should be able to do this in the DT core code. It doesn't matter
that these properties are arm* only. Other arches won't find the
properties.

Also, note that there is now a drivers/of/kexec.c (in -next) though
not sure if all this would go there or stay in fdt.c with the rest of
the memory parsing.

> +}
> +
> +#else
> +static inline void fdt_enforce_memory_region(void) { }
> +#endif
> +
> +#if defined(CONFIG_CRASH_DUMP) && defined(CONFIG_OF_EARLY_FLATTREE)
> +static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
> +               const char *uname, int depth, void *data)

Same comments as above.

> +{
> +       const __be32 *reg;
> +       int len;
> +
> +       if (depth != 1 || strcmp(uname, "chosen") != 0)
> +               return 0;
> +
> +       reg = of_get_flat_dt_prop(node, "linux,elfcorehdr", &len);
> +       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> +               return 1;
> +
> +       elfcorehdr_addr = dt_mem_next_cell(dt_root_addr_cells, &reg);
> +       elfcorehdr_size = dt_mem_next_cell(dt_root_size_cells, &reg);
> +       return 1;
> +}
> +
> +/*
> + * 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)
> +{
> +       of_scan_flat_dt(early_init_dt_scan_elfcorehdr, NULL);
> +
> +       if (!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);
> +}
> +#else
> +static inline void reserve_elfcorehdr(void) { }
> +#endif
> +
>  void __init arm_memblock_init(const struct machine_desc *mdesc)
>  {
> +       /* Handle linux,usable-memory-range property */
> +       fdt_enforce_memory_region();
> +
>         /* Register the kernel text, kernel data and initrd with memblock. */
>         memblock_reserve(__pa(KERNEL_START), KERNEL_END - KERNEL_START);
>
> @@ -225,6 +313,8 @@ 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
>

_______________________________________________
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kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

Re: [PATCH v3] ARM: Parse kdump DT properties

[Rob Herring]

On Wed, Mar 17, 2021 at 5:31 AM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
>
> 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@glider.be>
> ---
> 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@glider.be/
>
> 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,
> ---
>  Documentation/devicetree/bindings/chosen.txt  |  4 +-

Note that I've been meaning to remove this file because dtschema has a
schema replacing it.

>  .../arm/boot/compressed/fdt_check_mem_start.c | 48 ++++++++--
>  arch/arm/mm/init.c                            | 90 +++++++++++++++++++
>  3 files changed, 134 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
> index 45e79172a646c537..ba75c58413667760 100644
> --- a/Documentation/devicetree/bindings/chosen.txt
> +++ b/Documentation/devicetree/bindings/chosen.txt
> @@ -79,7 +79,7 @@ a different secondary CPU release mechanism)
>  linux,usable-memory-range
>  -------------------------
>
> -This property (arm64 only) holds a base address and size, describing a
> +This property (arm and arm64 only) holds a base address and size, describing a

I'd rather not have to change this again when RiscV gets around to
copying kdump support.

>  limited region in which memory may be considered available for use by
>  the kernel. Memory outside of this range is not available for use.
>
> @@ -106,7 +106,7 @@ respectively, of the root node.
>  linux,elfcorehdr
>  ----------------
>
> -This property (currently used only on arm64) holds the memory range,
> +This property (currently used only on arm and arm64) holds the memory range,
>  the address and the size, of the elf core header which mainly describes
>  the panicked kernel's memory layout as PT_LOAD segments of elf format.
>  e.g.
> 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 828a2561b2295813..d1ae15d9b29121e6 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>
> @@ -210,8 +211,95 @@ void check_cpu_icache_size(int cpuid)
>  }
>  #endif
>
> +#ifdef CONFIG_OF_EARLY_FLATTREE
> +static int __init early_init_dt_scan_usablemem(unsigned long node,
> +               const char *uname, int depth, void *data)
> +{
> +       struct memblock_region *usablemem = data;
> +       const __be32 *reg;
> +       int len;
> +
> +       if (depth != 1 || strcmp(uname, "chosen") != 0)
> +               return 0;

We have libfdt now, just get the '/chosen' node rather than using
of_scan_flat_dt().


> +
> +       reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
> +       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> +               return 1;
> +
> +       usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
> +       usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
> +       return 1;
> +}
> +
> +static void __init fdt_enforce_memory_region(void)
> +{
> +       struct memblock_region reg = {
> +               .size = 0,
> +       };
> +
> +       of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
> +
> +       if (reg.size)
> +               memblock_cap_memory_range(reg.base, reg.size);

We should be able to do this in the DT core code. It doesn't matter
that these properties are arm* only. Other arches won't find the
properties.

Also, note that there is now a drivers/of/kexec.c (in -next) though
not sure if all this would go there or stay in fdt.c with the rest of
the memory parsing.

> +}
> +
> +#else
> +static inline void fdt_enforce_memory_region(void) { }
> +#endif
> +
> +#if defined(CONFIG_CRASH_DUMP) && defined(CONFIG_OF_EARLY_FLATTREE)
> +static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
> +               const char *uname, int depth, void *data)

Same comments as above.

> +{
> +       const __be32 *reg;
> +       int len;
> +
> +       if (depth != 1 || strcmp(uname, "chosen") != 0)
> +               return 0;
> +
> +       reg = of_get_flat_dt_prop(node, "linux,elfcorehdr", &len);
> +       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> +               return 1;
> +
> +       elfcorehdr_addr = dt_mem_next_cell(dt_root_addr_cells, &reg);
> +       elfcorehdr_size = dt_mem_next_cell(dt_root_size_cells, &reg);
> +       return 1;
> +}
> +
> +/*
> + * 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)
> +{
> +       of_scan_flat_dt(early_init_dt_scan_elfcorehdr, NULL);
> +
> +       if (!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);
> +}
> +#else
> +static inline void reserve_elfcorehdr(void) { }
> +#endif
> +
>  void __init arm_memblock_init(const struct machine_desc *mdesc)
>  {
> +       /* Handle linux,usable-memory-range property */
> +       fdt_enforce_memory_region();
> +
>         /* Register the kernel text, kernel data and initrd with memblock. */
>         memblock_reserve(__pa(KERNEL_START), KERNEL_END - KERNEL_START);
>
> @@ -225,6 +313,8 @@ 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
>

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Re: [PATCH v3] ARM: Parse kdump DT properties

[Geert Uytterhoeven]

Hi Rob,

On Mon, Mar 22, 2021 at 5:59 PM Rob Herring <robh+dt@kernel.org> wrote:
> On Wed, Mar 17, 2021 at 5:31 AM Geert Uytterhoeven
> <geert+renesas@glider.be> wrote:
> > 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@glider.be>

> > --- 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>
> > @@ -210,8 +211,95 @@ void check_cpu_icache_size(int cpuid)
> >  }
> >  #endif
> >
> > +#ifdef CONFIG_OF_EARLY_FLATTREE
> > +static int __init early_init_dt_scan_usablemem(unsigned long node,
> > +               const char *uname, int depth, void *data)
> > +{
> > +       struct memblock_region *usablemem = data;
> > +       const __be32 *reg;
> > +       int len;
> > +
> > +       if (depth != 1 || strcmp(uname, "chosen") != 0)
> > +               return 0;
>
> We have libfdt now, just get the '/chosen' node rather than using
> of_scan_flat_dt().
>
>
> > +
> > +       reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
> > +       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> > +               return 1;
> > +
> > +       usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
> > +       usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
> > +       return 1;
> > +}
> > +
> > +static void __init fdt_enforce_memory_region(void)
> > +{
> > +       struct memblock_region reg = {
> > +               .size = 0,
> > +       };
> > +
> > +       of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
> > +
> > +       if (reg.size)
> > +               memblock_cap_memory_range(reg.base, reg.size);
>
> We should be able to do this in the DT core code. It doesn't matter
> that these properties are arm* only. Other arches won't find the
> properties.
>
> Also, note that there is now a drivers/of/kexec.c (in -next) though
> not sure if all this would go there or stay in fdt.c with the rest of
> the memory parsing.

It's gonna be the latter, as that file handles the FDT during early
kernel startup, for both normal and kdump kernels.

Despite the name, drivers/of/kexec.c is not for kexec, but for
kexec_file.  This is the "new" fancy syscall that prepares the DTB
for the new kernel itself, unlike the classic kexec syscall, where
userspace is responsible for preparing the DTB for the new kernel.

> > +#if defined(CONFIG_CRASH_DUMP) && defined(CONFIG_OF_EARLY_FLATTREE)
> > +static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
> > +               const char *uname, int depth, void *data)
>
> Same comments as above.

This one can indeed be handled easily by drivers/of/fdt.c.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v3] ARM: Parse kdump DT properties

[Geert Uytterhoeven]

Hi Rob,

On Mon, Mar 22, 2021 at 5:59 PM Rob Herring <robh+dt@kernel.org> wrote:
> On Wed, Mar 17, 2021 at 5:31 AM Geert Uytterhoeven
> <geert+renesas@glider.be> wrote:
> > 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@glider.be>

> > --- 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>
> > @@ -210,8 +211,95 @@ void check_cpu_icache_size(int cpuid)
> >  }
> >  #endif
> >
> > +#ifdef CONFIG_OF_EARLY_FLATTREE
> > +static int __init early_init_dt_scan_usablemem(unsigned long node,
> > +               const char *uname, int depth, void *data)
> > +{
> > +       struct memblock_region *usablemem = data;
> > +       const __be32 *reg;
> > +       int len;
> > +
> > +       if (depth != 1 || strcmp(uname, "chosen") != 0)
> > +               return 0;
>
> We have libfdt now, just get the '/chosen' node rather than using
> of_scan_flat_dt().
>
>
> > +
> > +       reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
> > +       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> > +               return 1;
> > +
> > +       usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
> > +       usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
> > +       return 1;
> > +}
> > +
> > +static void __init fdt_enforce_memory_region(void)
> > +{
> > +       struct memblock_region reg = {
> > +               .size = 0,
> > +       };
> > +
> > +       of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
> > +
> > +       if (reg.size)
> > +               memblock_cap_memory_range(reg.base, reg.size);
>
> We should be able to do this in the DT core code. It doesn't matter
> that these properties are arm* only. Other arches won't find the
> properties.
>
> Also, note that there is now a drivers/of/kexec.c (in -next) though
> not sure if all this would go there or stay in fdt.c with the rest of
> the memory parsing.

It's gonna be the latter, as that file handles the FDT during early
kernel startup, for both normal and kdump kernels.

Despite the name, drivers/of/kexec.c is not for kexec, but for
kexec_file.  This is the "new" fancy syscall that prepares the DTB
for the new kernel itself, unlike the classic kexec syscall, where
userspace is responsible for preparing the DTB for the new kernel.

> > +#if defined(CONFIG_CRASH_DUMP) && defined(CONFIG_OF_EARLY_FLATTREE)
> > +static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
> > +               const char *uname, int depth, void *data)
>
> Same comments as above.

This one can indeed be handled easily by drivers/of/fdt.c.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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Re: [PATCH v3] ARM: Parse kdump DT properties

[Geert Uytterhoeven]

Hi Rob,

On Mon, Mar 22, 2021 at 5:59 PM Rob Herring <robh+dt@kernel.org> wrote:
> On Wed, Mar 17, 2021 at 5:31 AM Geert Uytterhoeven
> <geert+renesas@glider.be> wrote:
> > 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@glider.be>

> > --- 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>
> > @@ -210,8 +211,95 @@ void check_cpu_icache_size(int cpuid)
> >  }
> >  #endif
> >
> > +#ifdef CONFIG_OF_EARLY_FLATTREE
> > +static int __init early_init_dt_scan_usablemem(unsigned long node,
> > +               const char *uname, int depth, void *data)
> > +{
> > +       struct memblock_region *usablemem = data;
> > +       const __be32 *reg;
> > +       int len;
> > +
> > +       if (depth != 1 || strcmp(uname, "chosen") != 0)
> > +               return 0;
>
> We have libfdt now, just get the '/chosen' node rather than using
> of_scan_flat_dt().
>
>
> > +
> > +       reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
> > +       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> > +               return 1;
> > +
> > +       usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
> > +       usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
> > +       return 1;
> > +}
> > +
> > +static void __init fdt_enforce_memory_region(void)
> > +{
> > +       struct memblock_region reg = {
> > +               .size = 0,
> > +       };
> > +
> > +       of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
> > +
> > +       if (reg.size)
> > +               memblock_cap_memory_range(reg.base, reg.size);
>
> We should be able to do this in the DT core code. It doesn't matter
> that these properties are arm* only. Other arches won't find the
> properties.
>
> Also, note that there is now a drivers/of/kexec.c (in -next) though
> not sure if all this would go there or stay in fdt.c with the rest of
> the memory parsing.

It's gonna be the latter, as that file handles the FDT during early
kernel startup, for both normal and kdump kernels.

Despite the name, drivers/of/kexec.c is not for kexec, but for
kexec_file.  This is the "new" fancy syscall that prepares the DTB
for the new kernel itself, unlike the classic kexec syscall, where
userspace is responsible for preparing the DTB for the new kernel.

> > +#if defined(CONFIG_CRASH_DUMP) && defined(CONFIG_OF_EARLY_FLATTREE)
> > +static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
> > +               const char *uname, int depth, void *data)
>
> Same comments as above.

This one can indeed be handled easily by drivers/of/fdt.c.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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Re: [PATCH v3] ARM: Parse kdump DT properties

[Linus Walleij]

On Wed, Mar 17, 2021 at 12:31 PM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:

> 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@glider.be>

I like the approach overall.

I see Rob has some comments that need adressing.

The chosen.txt file needs an example of how to use this so people
can intuitively get it right if they want to play with it, it was at least
the first question in my head: how does that look in practice?

Yours,
Linus Walleij

Re: [PATCH v3] ARM: Parse kdump DT properties

[Linus Walleij]

On Wed, Mar 17, 2021 at 12:31 PM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:

> 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@glider.be>

I like the approach overall.

I see Rob has some comments that need adressing.

The chosen.txt file needs an example of how to use this so people
can intuitively get it right if they want to play with it, it was at least
the first question in my head: how does that look in practice?

Yours,
Linus Walleij

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

Re: [PATCH v3] ARM: Parse kdump DT properties

[Linus Walleij]

On Wed, Mar 17, 2021 at 12:31 PM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:

> 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@glider.be>

I like the approach overall.

I see Rob has some comments that need adressing.

The chosen.txt file needs an example of how to use this so people
can intuitively get it right if they want to play with it, it was at least
the first question in my head: how does that look in practice?

Yours,
Linus Walleij

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linux-arm-kernel mailing list
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