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, 159 insertions, 0 deletions

diff --git a/scripts/extract-sys-certs.pl b/scripts/extract-sys-certs.pl
new file mode 100755
index 000000000..fa8ab1511
--- /dev/null
+++ b/scripts/extract-sys-certs.pl
@@ -0,0 +1,159 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0
+#
+use warnings;
+use strict;
+use Math::BigInt;
+use Fcntl "SEEK_SET";
+
+die "Format: $0 [-s <systemmap-file>] <vmlinux-file> <keyring-file>\n"
+    if ($#ARGV != 1 && $#ARGV != 3 ||
+	$#ARGV == 3 && $ARGV[0] ne "-s");
+
+my $sysmap = "";
+if ($#ARGV == 3) {
+    shift;
+    $sysmap = $ARGV[0];
+    shift;
+}
+
+my $vmlinux = $ARGV[0];
+my $keyring = $ARGV[1];
+
+#
+# Parse the vmlinux section table
+#
+open FD, "objdump -h $vmlinux |" || die $vmlinux;
+my @lines = <FD>;
+close(FD) || die $vmlinux;
+
+my @sections = ();
+
+foreach my $line (@lines) {
+    chomp($line);
+    if ($line =~ /\s*([0-9]+)\s+(\S+)\s+([0-9a-f]+)\s+([0-9a-f]+)\s+([0-9a-f]+)\s+([0-9a-f]+)\s+2[*][*]([0-9]+)/
+	) {
+	my $seg  = $1;
+	my $name = $2;
+	my $len  = Math::BigInt->new("0x" . $3);
+	my $vma  = Math::BigInt->new("0x" . $4);
+	my $lma  = Math::BigInt->new("0x" . $5);
+	my $foff = Math::BigInt->new("0x" . $6);
+	my $align = 2 ** $7;
+
+	push @sections, { name => $name,
+			  vma => $vma,
+			  len => $len,
+			  foff => $foff };
+    }
+}
+
+print "Have $#sections sections\n";
+
+#
+# Try and parse the vmlinux symbol table.  If the vmlinux file has been created
+# from a vmlinuz file with extract-vmlinux then the symbol table will be empty.
+#
+open FD, "nm $vmlinux 2>/dev/null |" || die $vmlinux;
+@lines = <FD>;
+close(FD) || die $vmlinux;
+
+my %symbols = ();
+my $nr_symbols = 0;
+
+sub parse_symbols(@) {
+    foreach my $line (@_) {
+	chomp($line);
+	if ($line =~ /([0-9a-f]+)\s([a-zA-Z])\s(\S+)/
+	    ) {
+	    my $addr = "0x" . $1;
+	    my $type = $2;
+	    my $name = $3;
+
+	    $symbols{$name} = $addr;
+	    $nr_symbols++;
+	}
+    }
+}
+parse_symbols(@lines);
+
+if ($nr_symbols == 0 && $sysmap ne "") {
+    print "No symbols in vmlinux, trying $sysmap\n";
+
+    open FD, "<$sysmap" || die $sysmap;
+    @lines = <FD>;
+    close(FD) || die $sysmap;
+    parse_symbols(@lines);
+}
+
+die "No symbols available\n"
+    if ($nr_symbols == 0);
+
+print "Have $nr_symbols symbols\n";
+
+die "Can't find system certificate list"
+    unless (exists($symbols{"__cert_list_start"}) &&
+	    exists($symbols{"system_certificate_list_size"}));
+
+my $start = Math::BigInt->new($symbols{"__cert_list_start"});
+my $end;
+my $size;
+my $size_sym = Math::BigInt->new($symbols{"system_certificate_list_size"});
+
+open FD, "<$vmlinux" || die $vmlinux;
+binmode(FD);
+
+my $s = undef;
+foreach my $sec (@sections) {
+    my $s_name = $sec->{name};
+    my $s_vma = $sec->{vma};
+    my $s_len = $sec->{len};
+    my $s_foff = $sec->{foff};
+    my $s_vend = $s_vma + $s_len;
+
+    next unless ($start >= $s_vma);
+    next if ($start >= $s_vend);
+
+    die "Certificate list size was not found on the same section\n"
+	if ($size_sym < $s_vma || $size_sym > $s_vend);
+
+    die "Cert object in multiple sections: ", $s_name, " and ", $s->{name}, "\n"
+	if ($s);
+
+    my $size_off = $size_sym -$s_vma + $s_foff;
+    my $packed;
+    die $vmlinux if (!defined(sysseek(FD, $size_off, SEEK_SET)));
+    sysread(FD, $packed, 8);
+    $size = unpack 'L!', $packed;
+    $end = $start + $size;
+
+    printf "Have %u bytes of certs at VMA 0x%x\n", $size, $start;
+
+    die "Cert object partially overflows section $s_name\n"
+	if ($end > $s_vend);
+
+    $s = $sec;
+}
+
+die "Cert object not inside a section\n"
+    unless ($s);
+
+print "Certificate list in section ", $s->{name}, "\n";
+
+my $foff = $start - $s->{vma} + $s->{foff};
+
+printf "Certificate list at file offset 0x%x\n", $foff;
+
+die $vmlinux if (!defined(sysseek(FD, $foff, SEEK_SET)));
+my $buf = "";
+my $len = sysread(FD, $buf, $size);
+die "$vmlinux" if (!defined($len));
+die "Short read on $vmlinux\n" if ($len != $size);
+close(FD) || die $vmlinux;
+
+open FD, ">$keyring" || die $keyring;
+binmode(FD);
+$len = syswrite(FD, $buf, $size);
+die "$keyring" if (!defined($len));
+die "Short write on $keyring\n" if ($len != $size);
+close(FD) || die $keyring;