sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 410 insertions, 0 deletions

diff --git a/scripts/insert-sys-cert.c b/scripts/insert-sys-cert.c
new file mode 100644
index 000000000..8902836c2
--- /dev/null
+++ b/scripts/insert-sys-cert.c
@@ -0,0 +1,410 @@
+/* Write the contents of the <certfile> into kernel symbol system_extra_cert
+ *
+ * Copyright (C) IBM Corporation, 2015
+ *
+ * Author: Mehmet Kayaalp <mkayaalp@linux.vnet.ibm.com>
+ *
+ * This software may be used and distributed according to the terms
+ * of the GNU General Public License, incorporated herein by reference.
+ *
+ * Usage: insert-sys-cert [-s <System.map> -b <vmlinux> -c <certfile>
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <ctype.h>
+#include <string.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <elf.h>
+
+#define CERT_SYM  "system_extra_cert"
+#define USED_SYM  "system_extra_cert_used"
+#define LSIZE_SYM "system_certificate_list_size"
+
+#define info(format, args...) fprintf(stderr, "INFO:    " format, ## args)
+#define warn(format, args...) fprintf(stdout, "WARNING: " format, ## args)
+#define  err(format, args...) fprintf(stderr, "ERROR:   " format, ## args)
+
+#if UINTPTR_MAX == 0xffffffff
+#define CURRENT_ELFCLASS ELFCLASS32
+#define Elf_Ehdr	Elf32_Ehdr
+#define Elf_Shdr	Elf32_Shdr
+#define Elf_Sym		Elf32_Sym
+#else
+#define CURRENT_ELFCLASS ELFCLASS64
+#define Elf_Ehdr	Elf64_Ehdr
+#define Elf_Shdr	Elf64_Shdr
+#define Elf_Sym		Elf64_Sym
+#endif
+
+static unsigned char endianness(void)
+{
+	uint16_t two_byte = 0x00FF;
+	uint8_t low_address = *((uint8_t *)&two_byte);
+
+	if (low_address == 0)
+		return ELFDATA2MSB;
+	else
+		return ELFDATA2LSB;
+}
+
+struct sym {
+	char *name;
+	unsigned long address;
+	unsigned long offset;
+	void *content;
+	int size;
+};
+
+static unsigned long get_offset_from_address(Elf_Ehdr *hdr, unsigned long addr)
+{
+	Elf_Shdr *x;
+	unsigned int i, num_sections;
+
+	x = (void *)hdr + hdr->e_shoff;
+	if (hdr->e_shnum == SHN_UNDEF)
+		num_sections = x[0].sh_size;
+	else
+		num_sections = hdr->e_shnum;
+
+	for (i = 1; i < num_sections; i++) {
+		unsigned long start = x[i].sh_addr;
+		unsigned long end = start + x[i].sh_size;
+		unsigned long offset = x[i].sh_offset;
+
+		if (addr >= start && addr <= end)
+			return addr - start + offset;
+	}
+	return 0;
+}
+
+
+#define LINE_SIZE 100
+
+static void get_symbol_from_map(Elf_Ehdr *hdr, FILE *f, char *name,
+				struct sym *s)
+{
+	char l[LINE_SIZE];
+	char *w, *p, *n;
+
+	s->size = 0;
+	s->address = 0;
+	s->offset = 0;
+	if (fseek(f, 0, SEEK_SET) != 0) {
+		perror("File seek failed");
+		exit(EXIT_FAILURE);
+	}
+	while (fgets(l, LINE_SIZE, f)) {
+		p = strchr(l, '\n');
+		if (!p) {
+			err("Missing line ending.\n");
+			return;
+		}
+		n = strstr(l, name);
+		if (n)
+			break;
+	}
+	if (!n) {
+		err("Unable to find symbol: %s\n", name);
+		return;
+	}
+	w = strchr(l, ' ');
+	if (!w)
+		return;
+
+	*w = '\0';
+	s->address = strtoul(l, NULL, 16);
+	if (s->address == 0)
+		return;
+	s->offset = get_offset_from_address(hdr, s->address);
+	s->name = name;
+	s->content = (void *)hdr + s->offset;
+}
+
+static Elf_Sym *find_elf_symbol(Elf_Ehdr *hdr, Elf_Shdr *symtab, char *name)
+{
+	Elf_Sym *sym, *symtab_start;
+	char *strtab, *symname;
+	unsigned int link;
+	Elf_Shdr *x;
+	int i, n;
+
+	x = (void *)hdr + hdr->e_shoff;
+	link = symtab->sh_link;
+	symtab_start = (void *)hdr + symtab->sh_offset;
+	n = symtab->sh_size / symtab->sh_entsize;
+	strtab = (void *)hdr + x[link].sh_offset;
+
+	for (i = 0; i < n; i++) {
+		sym = &symtab_start[i];
+		symname = strtab + sym->st_name;
+		if (strcmp(symname, name) == 0)
+			return sym;
+	}
+	err("Unable to find symbol: %s\n", name);
+	return NULL;
+}
+
+static void get_symbol_from_table(Elf_Ehdr *hdr, Elf_Shdr *symtab,
+				  char *name, struct sym *s)
+{
+	Elf_Shdr *sec;
+	int secndx;
+	Elf_Sym *elf_sym;
+	Elf_Shdr *x;
+
+	x = (void *)hdr + hdr->e_shoff;
+	s->size = 0;
+	s->address = 0;
+	s->offset = 0;
+	elf_sym = find_elf_symbol(hdr, symtab, name);
+	if (!elf_sym)
+		return;
+	secndx = elf_sym->st_shndx;
+	if (!secndx)
+		return;
+	sec = &x[secndx];
+	s->size = elf_sym->st_size;
+	s->address = elf_sym->st_value;
+	s->offset = s->address - sec->sh_addr
+			       + sec->sh_offset;
+	s->name = name;
+	s->content = (void *)hdr + s->offset;
+}
+
+static Elf_Shdr *get_symbol_table(Elf_Ehdr *hdr)
+{
+	Elf_Shdr *x;
+	unsigned int i, num_sections;
+
+	x = (void *)hdr + hdr->e_shoff;
+	if (hdr->e_shnum == SHN_UNDEF)
+		num_sections = x[0].sh_size;
+	else
+		num_sections = hdr->e_shnum;
+
+	for (i = 1; i < num_sections; i++)
+		if (x[i].sh_type == SHT_SYMTAB)
+			return &x[i];
+	return NULL;
+}
+
+static void *map_file(char *file_name, int *size)
+{
+	struct stat st;
+	void *map;
+	int fd;
+
+	fd = open(file_name, O_RDWR);
+	if (fd < 0) {
+		perror(file_name);
+		return NULL;
+	}
+	if (fstat(fd, &st)) {
+		perror("Could not determine file size");
+		close(fd);
+		return NULL;
+	}
+	*size = st.st_size;
+	map = mmap(NULL, *size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+	if (map == MAP_FAILED) {
+		perror("Mapping to memory failed");
+		close(fd);
+		return NULL;
+	}
+	close(fd);
+	return map;
+}
+
+static char *read_file(char *file_name, int *size)
+{
+	struct stat st;
+	char *buf;
+	int fd;
+
+	fd = open(file_name, O_RDONLY);
+	if (fd < 0) {
+		perror(file_name);
+		return NULL;
+	}
+	if (fstat(fd, &st)) {
+		perror("Could not determine file size");
+		close(fd);
+		return NULL;
+	}
+	*size = st.st_size;
+	buf = malloc(*size);
+	if (!buf) {
+		perror("Allocating memory failed");
+		close(fd);
+		return NULL;
+	}
+	if (read(fd, buf, *size) != *size) {
+		perror("File read failed");
+		close(fd);
+		return NULL;
+	}
+	close(fd);
+	return buf;
+}
+
+static void print_sym(Elf_Ehdr *hdr, struct sym *s)
+{
+	info("sym:    %s\n", s->name);
+	info("addr:   0x%lx\n", s->address);
+	info("size:   %d\n", s->size);
+	info("offset: 0x%lx\n", (unsigned long)s->offset);
+}
+
+static void print_usage(char *e)
+{
+	printf("Usage %s [-s <System.map>] -b <vmlinux> -c <certfile>\n", e);
+}
+
+int main(int argc, char **argv)
+{
+	char *system_map_file = NULL;
+	char *vmlinux_file = NULL;
+	char *cert_file = NULL;
+	int vmlinux_size;
+	int cert_size;
+	Elf_Ehdr *hdr;
+	char *cert;
+	FILE *system_map;
+	unsigned long *lsize;
+	int *used;
+	int opt;
+	Elf_Shdr *symtab = NULL;
+	struct sym cert_sym, lsize_sym, used_sym;
+
+	while ((opt = getopt(argc, argv, "b:c:s:")) != -1) {
+		switch (opt) {
+		case 's':
+			system_map_file = optarg;
+			break;
+		case 'b':
+			vmlinux_file = optarg;
+			break;
+		case 'c':
+			cert_file = optarg;
+			break;
+		default:
+			break;
+		}
+	}
+
+	if (!vmlinux_file || !cert_file) {
+		print_usage(argv[0]);
+		exit(EXIT_FAILURE);
+	}
+
+	cert = read_file(cert_file, &cert_size);
+	if (!cert)
+		exit(EXIT_FAILURE);
+
+	hdr = map_file(vmlinux_file, &vmlinux_size);
+	if (!hdr)
+		exit(EXIT_FAILURE);
+
+	if (vmlinux_size < sizeof(*hdr)) {
+		err("Invalid ELF file.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if ((hdr->e_ident[EI_MAG0] != ELFMAG0) ||
+	    (hdr->e_ident[EI_MAG1] != ELFMAG1) ||
+	    (hdr->e_ident[EI_MAG2] != ELFMAG2) ||
+	    (hdr->e_ident[EI_MAG3] != ELFMAG3)) {
+		err("Invalid ELF magic.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (hdr->e_ident[EI_CLASS] != CURRENT_ELFCLASS) {
+		err("ELF class mismatch.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (hdr->e_ident[EI_DATA] != endianness()) {
+		err("ELF endian mismatch.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (hdr->e_shoff > vmlinux_size) {
+		err("Could not find section header.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	symtab = get_symbol_table(hdr);
+	if (!symtab) {
+		warn("Could not find the symbol table.\n");
+		if (!system_map_file) {
+			err("Please provide a System.map file.\n");
+			print_usage(argv[0]);
+			exit(EXIT_FAILURE);
+		}
+
+		system_map = fopen(system_map_file, "r");
+		if (!system_map) {
+			perror(system_map_file);
+			exit(EXIT_FAILURE);
+		}
+		get_symbol_from_map(hdr, system_map, CERT_SYM, &cert_sym);
+		get_symbol_from_map(hdr, system_map, USED_SYM, &used_sym);
+		get_symbol_from_map(hdr, system_map, LSIZE_SYM, &lsize_sym);
+		cert_sym.size = used_sym.address - cert_sym.address;
+	} else {
+		info("Symbol table found.\n");
+		if (system_map_file)
+			warn("System.map is ignored.\n");
+		get_symbol_from_table(hdr, symtab, CERT_SYM, &cert_sym);
+		get_symbol_from_table(hdr, symtab, USED_SYM, &used_sym);
+		get_symbol_from_table(hdr, symtab, LSIZE_SYM, &lsize_sym);
+	}
+
+	if (!cert_sym.offset || !lsize_sym.offset || !used_sym.offset)
+		exit(EXIT_FAILURE);
+
+	print_sym(hdr, &cert_sym);
+	print_sym(hdr, &used_sym);
+	print_sym(hdr, &lsize_sym);
+
+	lsize = (unsigned long *)lsize_sym.content;
+	used = (int *)used_sym.content;
+
+	if (cert_sym.size < cert_size) {
+		err("Certificate is larger than the reserved area!\n");
+		exit(EXIT_FAILURE);
+	}
+
+	/* If the existing cert is the same, don't overwrite */
+	if (cert_size == *used &&
+	    strncmp(cert_sym.content, cert, cert_size) == 0) {
+		warn("Certificate was already inserted.\n");
+		exit(EXIT_SUCCESS);
+	}
+
+	if (*used > 0)
+		warn("Replacing previously inserted certificate.\n");
+
+	memcpy(cert_sym.content, cert, cert_size);
+	if (cert_size < cert_sym.size)
+		memset(cert_sym.content + cert_size,
+			0, cert_sym.size - cert_size);
+
+	*lsize = *lsize + cert_size - *used;
+	*used = cert_size;
+	info("Inserted the contents of %s into %lx.\n", cert_file,
+						cert_sym.address);
+	info("Used %d bytes out of %d bytes reserved.\n", *used,
+						 cert_sym.size);
+	exit(EXIT_SUCCESS);
+}