powerpc/kexec_load: add hotplug support

Kernel commits b741092d5976 ("powerpc/crash: add crash CPU hotplug
support") and 849599b702ef ("powerpc/crash: add crash memory hotplug
support") added crash CPU/Memory hotplug support on PowerPC. This patch
extends that support for the kexec_load syscall.

During CPU/Memory hotplug events on PowerPC, two kexec segments,
elfcorehdr, and FDT, get updated by the kernel. To ensure the kernel
can safely update these two kexec segments for the kdump image loaded
using the kexec_load system call, the following changes are made:

1. Extra size is allocated for both elfcorehdr and FDT to accommodate
   additional resources in the future. For the elfcorehdr, the size hint
   is taken from /sys/kernel/crash_elfcorehdr_size sysfs, while for FDT,
   extra size is allocated to hold possible CPU nodes.

2. Both elfcorehdr and FDT are skipped from SHA calculation.

Acked-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Simon Horman <horms@kernel.org>

kexec/arch/ppc64/crashdump-ppc64.c

@@ -476,7 +476,7 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline,
 				uint64_t max_addr, unsigned long min_base)
 {
 	void *tmp;
-	unsigned long sz;
+	unsigned long sz, memsz;
 	uint64_t elfcorehdr;
 	int nr_ranges, align = 1024, i;
 	unsigned long long end;
@@ -531,8 +531,18 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline,
 		}
 	}
 
-	elfcorehdr = add_buffer(info, tmp, sz, sz, align, min_base,
-				max_addr, 1);
+	memsz = sz;
+	/* To support --hotplug, replace the calculated memsz with the value
+	 * from /sys/kernel/crash_elfcorehdr_size and align it correctly.
+	 */
+	if (do_hotplug) {
+		if (elfcorehdrsz > sz)
+			memsz = _ALIGN(elfcorehdrsz, align);
+	}
+
+	/* Record the location of the elfcorehdr for hotplug handling */
+	info->elfcorehdr = elfcorehdr = add_buffer(info, tmp, sz, memsz, align,
+						   min_base, max_addr, 1);
 	reserve(elfcorehdr, sz);
 	/* modify and store the cmdline in a global array. This is later
 	 * read by flatten_device_tree and modified if required

kexec/arch/ppc64/fdt.c

@@ -17,6 +17,13 @@
 #include <libfdt.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <dirent.h>
+#include <sys/stat.h>
+
+#include "../../kexec.h"
+#include "../../kexec-syscall.h"
 
 /*
  * Let the kernel know it booted from kexec, as some things (e.g.
@@ -46,17 +53,244 @@ static int fixup_kexec_prop(void *fdt)
 	return 0;
 }
 
+static inline bool is_dot_dir(char * d_path)
+{
+	return d_path[0] == '.';
+}
+
+/*
+ * get_cpu_node_size - Returns size of files including file name size under
+ *                     the given @cpu_node_path.
+ */
+static int get_cpu_node_size(char *cpu_node_path)
+{
+	DIR *d;
+	struct dirent *de;
+	struct stat statbuf;
+	int cpu_node_size = 0;
+	char cpu_prop_path[2 * PATH_MAX];
+
+	d = opendir(cpu_node_path);
+	if (!d)
+		return 0;
+
+	while ((de = readdir(d)) != NULL) {
+		if (de->d_type != DT_REG)
+			continue;
+
+		memset(cpu_prop_path, '\0', PATH_MAX);
+		snprintf(cpu_prop_path, 2 * PATH_MAX, "%s/%s", cpu_node_path,
+			 de->d_name);
+
+		if (stat(cpu_prop_path, &statbuf))
+			continue;
+
+		cpu_node_size += statbuf.st_size;
+		cpu_node_size += strlen(de->d_name);
+	}
+
+	return cpu_node_size;
+}
+
+/*
+ * is_cpu_node - Checks if the node specified by the given @path
+ *               represents a CPU node.
+ *
+ * Returns true if the @path has a "device_type" file containing "cpu";
+ * otherwise, returns false.
+ */
+static bool is_cpu_node(char *path)
+{
+	FILE *file;
+	bool ret = false;
+	char device_type[4];
+
+	file = fopen(path, "r");
+	if (!file)
+		return false;
+
+	memset(device_type, '\0', 4);
+	if (fread(device_type, 1, 3, file) < 3)
+		goto out;
+
+	if (strcmp(device_type, "cpu"))
+		goto out;
+
+	ret = true;
+out:
+	fclose(file);
+	return ret;
+}
+
+static int get_threads_per_cpu(char *path)
+{
+	struct stat statbuf;
+	if (stat(path, &statbuf))
+		return 0;
+
+	return statbuf.st_size / 4;
+}
+
+/**
+ * get_present_cpus - finds the present CPUs in the system
+ *
+ * This function opens the file `/sys/devices/system/cpu/present` to read
+ * the range of present CPUs. It parses the range and calculates the
+ * total number of present CPUs in the system.
+ *
+ * Returns total number of present CPUs on success, -1 on failure.
+ */
+static int get_present_cpus()
+{
+	char *range;
+	char buf[1024];
+	int start, end;
+	int cpu_count = 0;
+	FILE *file = fopen("/sys/devices/system/cpu/present", "r");
+
+	if (!file)
+		return -1;
+
+	if (!fgets(buf, sizeof(buf), file))
+		return -1;
+
+	fclose(file);
+
+	range = strtok(buf, ",");
+	while (range != NULL) {
+		if (sscanf(range, "%d-%d", &start, &end) == 2) {
+			for (int i = start; i <= end; i++)
+				cpu_count++;
+		} else if (sscanf(range, "%d", &start) == 1) {
+			cpu_count++;
+		} else {
+			return -1;
+		}
+		range = strtok(NULL, ",");
+	}
+
+	return cpu_count;
+}
+
+/*
+ * get_cpu_info - Finds the following CPU attributes:
+ *
+ * threads_per_cpu: Number of threads per CPU, based on the device tree entry
+ *                  /proc/device-tree/cpus/<cpu_node>/ibm,ppc-interrupt-server#s.
+ * cpu_node_size: Size of files including file name size under a CPU node.
+ *
+ * Returns 0 on success, else -1.
+ */
+static int get_cpu_info(int *_present_cpus, int *_threads_per_cpu, int *_cpu_node_size)
+{
+	DIR *d;
+	struct dirent *de;
+	char path[PATH_MAX];
+	int present_cpus = 0, threads_per_cpu = 0, cpu_node_size = 0;
+	char *cpus_node_path = "/proc/device-tree/cpus";
+
+	present_cpus = get_present_cpus();
+	if (present_cpus < 0)
+		return -1;
+
+	d = opendir(cpus_node_path);
+	if (!d)
+		return -1;
+
+	while ((de = readdir(d)) != NULL) {
+		if ((de->d_type != DT_DIR) || is_dot_dir(de->d_name))
+			continue;
+
+		memset(path, '\0', PATH_MAX);
+		snprintf(path, PATH_MAX, "%s/%s/%s", cpus_node_path,
+			 de->d_name, "device_type");
+
+		/* Skip nodes with device_type != "cpu" */
+		if (!is_cpu_node(path))
+			continue;
+
+		/*
+		 * Found the first node under /proc/device-tree/cpus with
+		 * device_type == "cpu"
+		 */
+		memset(path, '\0', PATH_MAX);
+		snprintf(path, PATH_MAX, "%s/%s", cpus_node_path, de->d_name);
+		cpu_node_size = get_cpu_node_size(path);
+
+		memset(path, '\0', PATH_MAX);
+		snprintf(path, PATH_MAX, "%s/%s/%s", cpus_node_path,
+		de->d_name, "ibm,ppc-interrupt-server#s");
+		threads_per_cpu = get_threads_per_cpu(path);
+		break;
+	}
+
+	closedir(d);
+
+	if (!(threads_per_cpu && cpu_node_size))
+		return -1;
+
+	*_present_cpus = present_cpus;
+	*_cpu_node_size = cpu_node_size;
+	*_threads_per_cpu = threads_per_cpu;
+
+	dbgprintf("present_cpus: %d, threads_per_cpu: %d, cpu_node_size: %d\n",
+		  present_cpus, threads_per_cpu, cpu_node_size);
+
+	return 0;
+}
+
+/*
+ * kdump_fdt_extra_size - Calculates the extra size needed for the Flattened
+ *                        Device Tree (FDT) based on the possible and present
+ *                        CPUs in the system.
+ */
+static unsigned int kdump_fdt_extra_size(void)
+{
+	int cpus_in_system;
+	unsigned int extra_size = 0;
+	int present_cpus = 0, threads_per_cpu = 0, cpu_node_size = 0;
+	int possible_cpus;
+
+	/* ALL possible CPUs are present in FDT so no extra size required */
+	if (sysconf(_SC_NPROCESSORS_ONLN) == sysconf(_SC_NPROCESSORS_CONF))
+		return 0;
+
+	if (get_cpu_info(&present_cpus, &threads_per_cpu, &cpu_node_size)) {
+		die("Failed to get cpu info\n");
+	}
+
+	cpus_in_system = present_cpus / threads_per_cpu;
+	possible_cpus = sysconf(_SC_NPROCESSORS_CONF) / threads_per_cpu;
+	dbgprintf("cpus_in_system: %d, possible_cpus: %d\n", cpus_in_system,
+		  possible_cpus);
+
+	if (cpus_in_system > possible_cpus)
+		die("Possible CPU nodes can't be less than active CPU nodes\n");
+
+	extra_size = (possible_cpus - cpus_in_system) * cpu_node_size;
+	dbgprintf("kdump fdt extra size: %u\n", extra_size);
+
+	return extra_size;
+}
 
 /*
  * For now, assume that the added content fits in the file.
  * This should be the case when flattening from /proc/device-tree,
  * and when passing in a dtb, dtc can be told to add padding.
  */
-int fixup_dt(char **fdt, off_t *size)
+int fixup_dt(char **fdt, off_t *size, unsigned long kexec_flags)
 {
 	int ret;
 
 	*size += 4096;
+
+	/* To support --hotplug option for the kexec_load syscall, consider
+	 * adding extra buffer to FDT so that the kernel can add CPU nodes
+	 * of hot-added CPUs.
+	 */
+	if (do_hotplug && (kexec_flags & KEXEC_ON_CRASH))
+		*size += kdump_fdt_extra_size();
+
 	*fdt = realloc(*fdt, *size);
 	if (!*fdt) {
 		fprintf(stderr, "%s: out of memory\n", __func__);

kexec/arch/ppc64/include/arch/fdt.h

@@ -3,6 +3,6 @@
 
 #include <sys/types.h>
 
-int fixup_dt(char **fdt, off_t *size);
+int fixup_dt(char **fdt, off_t *size, unsigned long kexec_flags);
 
 #endif

kexec/arch/ppc64/kexec-elf-ppc64.c

@@ -345,7 +345,7 @@ int elf_ppc64_load(int argc, char **argv, const char *buf, off_t len,
 		create_flatten_tree(&seg_buf, &seg_size, cmdline);
 	}
 
-	result = fixup_dt(&seg_buf, &seg_size);
+	result = fixup_dt(&seg_buf, &seg_size, info->kexec_flags);
 	if (result < 0)
 		return result;
 

kexec/arch/ppc64/kexec-ppc64.c

@@ -24,6 +24,7 @@
 #include <errno.h>
 #include <stdint.h>
 #include <string.h>
+#include <libfdt.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <dirent.h>
@@ -968,7 +969,13 @@ void arch_update_purgatory(struct kexec_info *UNUSED(info))
 {
 }
 
-int arch_do_exclude_segment(struct kexec_info *UNUSED(info), struct kexec_segment *UNUSED(segment))
+int arch_do_exclude_segment(struct kexec_info *info, struct kexec_segment *segment)
 {
+	if (info->elfcorehdr == (unsigned long) segment->mem)
+		return 1;
+
+	if (segment->buf && fdt_magic(segment->buf) == FDT_MAGIC)
+		return 1;
+
 	return 0;
 }