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>

2 files changed, 437 insertions, 0 deletions

diff --git a/arch/alpha/boot/tools/mkbb.c b/arch/alpha/boot/tools/mkbb.c
new file mode 100644
index 000000000..fc47f33f8
--- /dev/null
+++ b/arch/alpha/boot/tools/mkbb.c
@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: GPL-2.0
+/* This utility makes a bootblock suitable for the SRM console/miniloader */
+
+/* Usage:
+ *	mkbb <device> <lxboot>
+ *
+ * Where <device> is the name of the device to install the bootblock on,
+ * and <lxboot> is the name of a bootblock to merge in.  This bootblock
+ * contains the offset and size of the bootloader.  It must be exactly
+ * 512 bytes long.
+ */
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+/* Minimal definition of disklabel, so we don't have to include
+ * asm/disklabel.h (confuses make)
+ */
+#ifndef MAXPARTITIONS
+#define MAXPARTITIONS   8                       /* max. # of partitions */
+#endif
+
+#ifndef u8
+#define u8 unsigned char
+#endif
+
+#ifndef u16
+#define u16 unsigned short
+#endif
+
+#ifndef u32
+#define u32 unsigned int
+#endif
+
+struct disklabel {
+    u32	d_magic;				/* must be DISKLABELMAGIC */
+    u16	d_type, d_subtype;
+    u8	d_typename[16];
+    u8	d_packname[16];
+    u32	d_secsize;
+    u32	d_nsectors;
+    u32	d_ntracks;
+    u32	d_ncylinders;
+    u32	d_secpercyl;
+    u32	d_secprtunit;
+    u16	d_sparespertrack;
+    u16	d_sparespercyl;
+    u32	d_acylinders;
+    u16	d_rpm, d_interleave, d_trackskew, d_cylskew;
+    u32	d_headswitch, d_trkseek, d_flags;
+    u32	d_drivedata[5];
+    u32	d_spare[5];
+    u32	d_magic2;				/* must be DISKLABELMAGIC */
+    u16	d_checksum;
+    u16	d_npartitions;
+    u32	d_bbsize, d_sbsize;
+    struct d_partition {
+	u32	p_size;
+	u32	p_offset;
+	u32	p_fsize;
+	u8	p_fstype;
+	u8	p_frag;
+	u16	p_cpg;
+    } d_partitions[MAXPARTITIONS];
+};
+
+
+typedef union __bootblock {
+    struct {
+        char			__pad1[64];
+        struct disklabel	__label;
+    } __u1;
+    struct {
+	unsigned long		__pad2[63];
+	unsigned long		__checksum;
+    } __u2;
+    char		bootblock_bytes[512];
+    unsigned long	bootblock_quadwords[64];
+} bootblock;
+
+#define	bootblock_label		__u1.__label
+#define bootblock_checksum	__u2.__checksum
+
+int main(int argc, char ** argv)
+{
+    bootblock		bootblock_from_disk;
+    bootblock		bootloader_image;
+    int			dev, fd;
+    int			i;
+    int			nread;
+
+    /* Make sure of the arg count */
+    if(argc != 3) {
+	fprintf(stderr, "Usage: %s device lxboot\n", argv[0]);
+	exit(0);
+    }
+
+    /* First, open the device and make sure it's accessible */
+    dev = open(argv[1], O_RDWR);
+    if(dev < 0) {
+	perror(argv[1]);
+	exit(0);
+    }
+
+    /* Now open the lxboot and make sure it's reasonable */
+    fd = open(argv[2], O_RDONLY);
+    if(fd < 0) {
+	perror(argv[2]);
+	close(dev);
+	exit(0);
+    }
+
+    /* Read in the lxboot */
+    nread = read(fd, &bootloader_image, sizeof(bootblock));
+    if(nread != sizeof(bootblock)) {
+	perror("lxboot read");
+	fprintf(stderr, "expected %zd, got %d\n", sizeof(bootblock), nread);
+	exit(0);
+    }
+
+    /* Read in the bootblock from disk. */
+    nread = read(dev, &bootblock_from_disk, sizeof(bootblock));
+    if(nread != sizeof(bootblock)) {
+	perror("bootblock read");
+	fprintf(stderr, "expected %zd, got %d\n", sizeof(bootblock), nread);
+	exit(0);
+    }
+
+    /* Swap the bootblock's disklabel into the bootloader */
+    bootloader_image.bootblock_label = bootblock_from_disk.bootblock_label;
+
+    /* Calculate the bootblock checksum */
+    bootloader_image.bootblock_checksum = 0;
+    for(i = 0; i < 63; i++) {
+	bootloader_image.bootblock_checksum += 
+			bootloader_image.bootblock_quadwords[i];
+    }
+
+    /* Write the whole thing out! */
+    lseek(dev, 0L, SEEK_SET);
+    if(write(dev, &bootloader_image, sizeof(bootblock)) != sizeof(bootblock)) {
+	perror("bootblock write");
+	exit(0);
+    }
+
+    close(fd);
+    close(dev);
+    exit(0);
+}
+
+
diff --git a/arch/alpha/boot/tools/objstrip.c b/arch/alpha/boot/tools/objstrip.c
new file mode 100644
index 000000000..7cf92d172
--- /dev/null
+++ b/arch/alpha/boot/tools/objstrip.c
@@ -0,0 +1,284 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * arch/alpha/boot/tools/objstrip.c
+ *
+ * Strip the object file headers/trailers from an executable (ELF or ECOFF).
+ *
+ * Copyright (C) 1996 David Mosberger-Tang.
+ */
+/*
+ * Converts an ECOFF or ELF object file into a bootable file.  The
+ * object file must be a OMAGIC file (i.e., data and bss follow immediately
+ * behind the text).  See DEC "Assembly Language Programmer's Guide"
+ * documentation for details.  The SRM boot process is documented in
+ * the Alpha AXP Architecture Reference Manual, Second Edition by
+ * Richard L. Sites and Richard T. Witek.
+ */
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <sys/fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include <linux/a.out.h>
+#include <linux/coff.h>
+#include <linux/param.h>
+#ifdef __ELF__
+# include <linux/elf.h>
+# define elfhdr elf64_hdr
+# define elf_phdr elf64_phdr
+# define elf_check_arch(x) ((x)->e_machine == EM_ALPHA)
+#endif
+
+/* bootfile size must be multiple of BLOCK_SIZE: */
+#define BLOCK_SIZE	512
+
+const char * prog_name;
+
+
+static void
+usage (void)
+{
+    fprintf(stderr,
+	    "usage: %s [-v] -p file primary\n"
+	    "       %s [-vb] file [secondary]\n", prog_name, prog_name);
+    exit(1);
+}
+
+
+int
+main (int argc, char *argv[])
+{
+    size_t nwritten, tocopy, n, mem_size, fil_size, pad = 0;
+    int fd, ofd, i, j, verbose = 0, primary = 0;
+    char buf[8192], *inname;
+    struct exec * aout;		/* includes file & aout header */
+    long offset;
+#ifdef __ELF__
+    struct elfhdr *elf;
+    struct elf_phdr *elf_phdr;	/* program header */
+    unsigned long long e_entry;
+#endif
+
+    prog_name = argv[0];
+
+    for (i = 1; i < argc && argv[i][0] == '-'; ++i) {
+	for (j = 1; argv[i][j]; ++j) {
+	    switch (argv[i][j]) {
+	      case 'v':
+		  verbose = ~verbose;
+		  break;
+
+	      case 'b':
+		  pad = BLOCK_SIZE;
+		  break;
+
+	      case 'p':
+		  primary = 1;		/* make primary bootblock */
+		  break;
+	    }
+	}
+    }
+
+    if (i >= argc) {
+	usage();
+    }
+    inname = argv[i++];
+
+    fd = open(inname, O_RDONLY);
+    if (fd == -1) {
+	perror("open");
+	exit(1);
+    }
+
+    ofd = 1;
+    if (i < argc) {
+	ofd = open(argv[i++], O_WRONLY | O_CREAT | O_TRUNC, 0666);
+	if (ofd == -1) {
+	    perror("open");
+	    exit(1);
+	}
+    }
+
+    if (primary) {
+	/* generate bootblock for primary loader */
+	
+	unsigned long bb[64], sum = 0;
+	struct stat st;
+	off_t size;
+	int i;
+
+	if (ofd == 1) {
+	    usage();
+	}
+
+	if (fstat(fd, &st) == -1) {
+	    perror("fstat");
+	    exit(1);
+	}
+
+	size = (st.st_size + BLOCK_SIZE - 1) & ~(BLOCK_SIZE - 1);
+	memset(bb, 0, sizeof(bb));
+	strcpy((char *) bb, "Linux SRM bootblock");
+	bb[60] = size / BLOCK_SIZE;	/* count */
+	bb[61] = 1;			/* starting sector # */
+	bb[62] = 0;			/* flags---must be 0 */
+	for (i = 0; i < 63; ++i) {
+	    sum += bb[i];
+	}
+	bb[63] = sum;
+	if (write(ofd, bb, sizeof(bb)) != sizeof(bb)) {
+	    perror("boot-block write");
+	    exit(1);
+	}
+	printf("%lu\n", size);
+	return 0;
+    }
+
+    /* read and inspect exec header: */
+
+    if (read(fd, buf, sizeof(buf)) < 0) {
+	perror("read");
+	exit(1);
+    }
+
+#ifdef __ELF__
+    elf = (struct elfhdr *) buf;
+
+    if (memcmp(&elf->e_ident[EI_MAG0], ELFMAG, SELFMAG) == 0) {
+	if (elf->e_type != ET_EXEC) {
+	    fprintf(stderr, "%s: %s is not an ELF executable\n",
+		    prog_name, inname);
+	    exit(1);
+	}
+	if (!elf_check_arch(elf)) {
+	    fprintf(stderr, "%s: is not for this processor (e_machine=%d)\n",
+		    prog_name, elf->e_machine);
+	    exit(1);
+	}
+	if (elf->e_phnum != 1) {
+	    fprintf(stderr,
+		    "%s: %d program headers (forgot to link with -N?)\n",
+		    prog_name, elf->e_phnum);
+	}
+
+	e_entry = elf->e_entry;
+
+	lseek(fd, elf->e_phoff, SEEK_SET);
+	if (read(fd, buf, sizeof(*elf_phdr)) != sizeof(*elf_phdr)) {
+	    perror("read");
+	    exit(1);
+	}
+
+	elf_phdr = (struct elf_phdr *) buf;
+	offset	 = elf_phdr->p_offset;
+	mem_size = elf_phdr->p_memsz;
+	fil_size = elf_phdr->p_filesz;
+
+	/* work around ELF bug: */
+	if (elf_phdr->p_vaddr < e_entry) {
+	    unsigned long delta = e_entry - elf_phdr->p_vaddr;
+	    offset   += delta;
+	    mem_size -= delta;
+	    fil_size -= delta;
+	    elf_phdr->p_vaddr += delta;
+	}
+
+	if (verbose) {
+	    fprintf(stderr, "%s: extracting %#016lx-%#016lx (at %lx)\n",
+		    prog_name, (long) elf_phdr->p_vaddr,
+		    elf_phdr->p_vaddr + fil_size, offset);
+	}
+    } else
+#endif
+    {
+	aout = (struct exec *) buf;
+
+	if (!(aout->fh.f_flags & COFF_F_EXEC)) {
+	    fprintf(stderr, "%s: %s is not in executable format\n",
+		    prog_name, inname);
+	    exit(1);
+	}
+
+	if (aout->fh.f_opthdr != sizeof(aout->ah)) {
+	    fprintf(stderr, "%s: %s has unexpected optional header size\n",
+		    prog_name, inname);
+	    exit(1);
+	}
+
+	if (N_MAGIC(*aout) != OMAGIC) {
+	    fprintf(stderr, "%s: %s is not an OMAGIC file\n",
+		    prog_name, inname);
+	    exit(1);
+	}
+	offset = N_TXTOFF(*aout);
+	fil_size = aout->ah.tsize + aout->ah.dsize;
+	mem_size = fil_size + aout->ah.bsize;
+
+	if (verbose) {
+	    fprintf(stderr, "%s: extracting %#016lx-%#016lx (at %lx)\n",
+		    prog_name, aout->ah.text_start,
+		    aout->ah.text_start + fil_size, offset);
+	}
+    }
+
+    if (lseek(fd, offset, SEEK_SET) != offset) {
+	perror("lseek");
+	exit(1);
+    }
+
+    if (verbose) {
+	fprintf(stderr, "%s: copying %lu byte from %s\n",
+		prog_name, (unsigned long) fil_size, inname);
+    }
+
+    tocopy = fil_size;
+    while (tocopy > 0) {
+	n = tocopy;
+	if (n > sizeof(buf)) {
+	    n = sizeof(buf);
+	}
+	tocopy -= n;
+	if ((size_t) read(fd, buf, n) != n) {
+	    perror("read");
+	    exit(1);
+	}
+	do {
+	    nwritten = write(ofd, buf, n);
+	    if ((ssize_t) nwritten == -1) {
+		perror("write");
+		exit(1);
+	    }
+	    n -= nwritten;
+	} while (n > 0);
+    }
+
+    if (pad) {
+	mem_size = ((mem_size + pad - 1) / pad) * pad;
+    }
+
+    tocopy = mem_size - fil_size;
+    if (tocopy > 0) {
+	fprintf(stderr,
+		"%s: zero-filling bss and aligning to %lu with %lu bytes\n",
+		prog_name, pad, (unsigned long) tocopy);
+
+	memset(buf, 0x00, sizeof(buf));
+	do {
+	    n = tocopy;
+	    if (n > sizeof(buf)) {
+		n = sizeof(buf);
+	    }
+	    nwritten = write(ofd, buf, n);
+	    if ((ssize_t) nwritten == -1) {
+		perror("write");
+		exit(1);
+	    }
+	    tocopy -= nwritten;
+	} while (tocopy > 0);
+    }
+    return 0;
+}