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, 138 insertions, 0 deletions

diff --git a/scripts/extract-module-sig.pl b/scripts/extract-module-sig.pl
new file mode 100755
index 000000000..36a2f59c4
--- /dev/null
+++ b/scripts/extract-module-sig.pl
@@ -0,0 +1,138 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0
+#
+# extract-mod-sig <part> <module-file>
+#
+# Reads the module file and writes out some or all of the signature
+# section to stdout.  Part is the bit to be written and is one of:
+#
+#  -0: The unsigned module, no signature data at all
+#  -a: All of the signature data, including magic number
+#  -d: Just the descriptor values as a sequence of numbers
+#  -n: Just the signer's name
+#  -k: Just the key ID
+#  -s: Just the crypto signature or PKCS#7 message
+#
+use warnings;
+use strict;
+
+die "Format: $0 -[0adnks] module-file >out\n"
+    if ($#ARGV != 1);
+
+my $part = $ARGV[0];
+my $modfile = $ARGV[1];
+
+my $magic_number = "~Module signature appended~\n";
+
+#
+# Read the module contents
+#
+open FD, "<$modfile" || die $modfile;
+binmode(FD);
+my @st = stat(FD);
+die "$modfile" unless (@st);
+my $buf = "";
+my $len = sysread(FD, $buf, $st[7]);
+die "$modfile" unless (defined($len));
+die "Short read on $modfile\n" unless ($len == $st[7]);
+close(FD) || die $modfile;
+
+print STDERR "Read ", $len, " bytes from module file\n";
+
+die "The file is too short to have a sig magic number and descriptor\n"
+    if ($len < 12 + length($magic_number));
+
+#
+# Check for the magic number and extract the information block
+#
+my $p = $len - length($magic_number);
+my $raw_magic = substr($buf, $p);
+
+die "Magic number not found at $len\n"
+    if ($raw_magic ne $magic_number);
+print STDERR "Found magic number at $len\n";
+
+$p -= 12;
+my $raw_info = substr($buf, $p, 12);
+
+my @info = unpack("CCCCCxxxN", $raw_info);
+my ($algo, $hash, $id_type, $name_len, $kid_len, $sig_len) = @info;
+
+if ($id_type == 0) {
+    print STDERR "Found PGP key identifier\n";
+} elsif ($id_type == 1) {
+    print STDERR "Found X.509 cert identifier\n";
+} elsif ($id_type == 2) {
+    print STDERR "Found PKCS#7/CMS encapsulation\n";
+} else {
+    print STDERR "Found unsupported identifier type $id_type\n";
+}
+
+#
+# Extract the three pieces of info data
+#
+die "Insufficient name+kid+sig data in file\n"
+    unless ($p >= $name_len + $kid_len + $sig_len);
+
+$p -= $sig_len;
+my $raw_sig = substr($buf, $p, $sig_len);
+$p -= $kid_len;
+my $raw_kid = substr($buf, $p, $kid_len);
+$p -= $name_len;
+my $raw_name = substr($buf, $p, $name_len);
+
+my $module_len = $p;
+
+if ($sig_len > 0) {
+    print STDERR "Found $sig_len bytes of signature [";
+    my $n = $sig_len > 16 ? 16 : $sig_len;
+    foreach my $i (unpack("C" x $n, substr($raw_sig, 0, $n))) {
+	printf STDERR "%02x", $i;
+    }
+    print STDERR "]\n";
+}
+
+if ($kid_len > 0) {
+    print STDERR "Found $kid_len bytes of key identifier [";
+    my $n = $kid_len > 16 ? 16 : $kid_len;
+    foreach my $i (unpack("C" x $n, substr($raw_kid, 0, $n))) {
+	printf STDERR "%02x", $i;
+    }
+    print STDERR "]\n";
+}
+
+if ($name_len > 0) {
+    print STDERR "Found $name_len bytes of signer's name [$raw_name]\n";
+}
+
+#
+# Produce the requested output
+#
+if ($part eq "-0") {
+    # The unsigned module, no signature data at all
+    binmode(STDOUT);
+    print substr($buf, 0, $module_len);
+} elsif ($part eq "-a") {
+    # All of the signature data, including magic number
+    binmode(STDOUT);
+    print substr($buf, $module_len);
+} elsif ($part eq "-d") {
+    # Just the descriptor values as a sequence of numbers
+    print join(" ", @info), "\n";
+} elsif ($part eq "-n") {
+    # Just the signer's name
+    print STDERR "No signer's name for PKCS#7 message type sig\n"
+	if ($id_type == 2);
+    binmode(STDOUT);
+    print $raw_name;
+} elsif ($part eq "-k") {
+    # Just the key identifier
+    print STDERR "No key ID for PKCS#7 message type sig\n"
+	if ($id_type == 2);
+    binmode(STDOUT);
+    print $raw_kid;
+} elsif ($part eq "-s") {
+    # Just the crypto signature or PKCS#7 message
+    binmode(STDOUT);
+    print $raw_sig;
+}