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, 40 insertions, 0 deletions

diff --git a/include/crypto/internal/simd.h b/include/crypto/internal/simd.h
new file mode 100644
index 000000000..f5e5d7b63
--- /dev/null
+++ b/include/crypto/internal/simd.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Shared crypto simd helpers
+ */
+
+#ifndef _CRYPTO_INTERNAL_SIMD_H
+#define _CRYPTO_INTERNAL_SIMD_H
+
+#include <asm/simd.h>
+#include <linux/percpu.h>
+#include <linux/types.h>
+
+struct simd_aead_alg;
+struct aead_alg;
+
+int simd_register_aeads_compat(struct aead_alg *algs, int count,
+			       struct simd_aead_alg **simd_algs);
+
+void simd_unregister_aeads(struct aead_alg *algs, int count,
+			   struct simd_aead_alg **simd_algs);
+
+/*
+ * crypto_simd_usable() - is it allowed at this time to use SIMD instructions or
+ *			  access the SIMD register file?
+ *
+ * This delegates to may_use_simd(), except that this also returns false if SIMD
+ * in crypto code has been temporarily disabled on this CPU by the crypto
+ * self-tests, in order to test the no-SIMD fallback code.  This override is
+ * currently limited to configurations where the "full" self-tests are enabled,
+ * because it might be a bit too invasive to be part of the "fast" self-tests.
+ */
+#ifdef CONFIG_CRYPTO_SELFTESTS_FULL
+DECLARE_PER_CPU(bool, crypto_simd_disabled_for_test);
+#define crypto_simd_usable() \
+	(may_use_simd() && !this_cpu_read(crypto_simd_disabled_for_test))
+#else
+#define crypto_simd_usable() may_use_simd()
+#endif
+
+#endif /* _CRYPTO_INTERNAL_SIMD_H */