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, 156 insertions, 0 deletions

diff --git a/include/crypto/blake2b.h b/include/crypto/blake2b.h
new file mode 100644
index 000000000..3bc37fd10
--- /dev/null
+++ b/include/crypto/blake2b.h
@@ -0,0 +1,156 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+
+#ifndef _CRYPTO_BLAKE2B_H
+#define _CRYPTO_BLAKE2B_H
+
+#include <linux/bug.h>
+#include <linux/types.h>
+#include <linux/string.h>
+
+enum blake2b_lengths {
+	BLAKE2B_BLOCK_SIZE = 128,
+	BLAKE2B_HASH_SIZE = 64,
+	BLAKE2B_KEY_SIZE = 64,
+
+	BLAKE2B_160_HASH_SIZE = 20,
+	BLAKE2B_256_HASH_SIZE = 32,
+	BLAKE2B_384_HASH_SIZE = 48,
+	BLAKE2B_512_HASH_SIZE = 64,
+};
+
+/**
+ * struct blake2b_ctx - Context for hashing a message with BLAKE2b
+ * @h: compression function state
+ * @t: block counter
+ * @f: finalization indicator
+ * @buf: partial block buffer; 'buflen' bytes are valid
+ * @buflen: number of bytes buffered in @buf
+ * @outlen: length of output hash value in bytes, at most BLAKE2B_HASH_SIZE
+ */
+struct blake2b_ctx {
+	/* 'h', 't', and 'f' are used in assembly code, so keep them as-is. */
+	u64 h[8];
+	u64 t[2];
+	u64 f[2];
+	u8 buf[BLAKE2B_BLOCK_SIZE];
+	unsigned int buflen;
+	unsigned int outlen;
+};
+
+enum blake2b_iv {
+	BLAKE2B_IV0 = 0x6A09E667F3BCC908ULL,
+	BLAKE2B_IV1 = 0xBB67AE8584CAA73BULL,
+	BLAKE2B_IV2 = 0x3C6EF372FE94F82BULL,
+	BLAKE2B_IV3 = 0xA54FF53A5F1D36F1ULL,
+	BLAKE2B_IV4 = 0x510E527FADE682D1ULL,
+	BLAKE2B_IV5 = 0x9B05688C2B3E6C1FULL,
+	BLAKE2B_IV6 = 0x1F83D9ABFB41BD6BULL,
+	BLAKE2B_IV7 = 0x5BE0CD19137E2179ULL,
+};
+
+static inline void __blake2b_init(struct blake2b_ctx *ctx, size_t outlen,
+				  const void *key, size_t keylen)
+{
+	ctx->h[0] = BLAKE2B_IV0 ^ (0x01010000 | keylen << 8 | outlen);
+	ctx->h[1] = BLAKE2B_IV1;
+	ctx->h[2] = BLAKE2B_IV2;
+	ctx->h[3] = BLAKE2B_IV3;
+	ctx->h[4] = BLAKE2B_IV4;
+	ctx->h[5] = BLAKE2B_IV5;
+	ctx->h[6] = BLAKE2B_IV6;
+	ctx->h[7] = BLAKE2B_IV7;
+	ctx->t[0] = 0;
+	ctx->t[1] = 0;
+	ctx->f[0] = 0;
+	ctx->f[1] = 0;
+	ctx->buflen = 0;
+	ctx->outlen = outlen;
+	if (keylen) {
+		memcpy(ctx->buf, key, keylen);
+		memset(&ctx->buf[keylen], 0, BLAKE2B_BLOCK_SIZE - keylen);
+		ctx->buflen = BLAKE2B_BLOCK_SIZE;
+	}
+}
+
+/**
+ * blake2b_init() - Initialize a BLAKE2b context for a new message (unkeyed)
+ * @ctx: the context to initialize
+ * @outlen: length of output hash value in bytes, at most BLAKE2B_HASH_SIZE
+ *
+ * Context: Any context.
+ */
+static inline void blake2b_init(struct blake2b_ctx *ctx, size_t outlen)
+{
+	__blake2b_init(ctx, outlen, NULL, 0);
+}
+
+/**
+ * blake2b_init_key() - Initialize a BLAKE2b context for a new message (keyed)
+ * @ctx: the context to initialize
+ * @outlen: length of output hash value in bytes, at most BLAKE2B_HASH_SIZE
+ * @key: the key
+ * @keylen: the key length in bytes, at most BLAKE2B_KEY_SIZE
+ *
+ * Context: Any context.
+ */
+static inline void blake2b_init_key(struct blake2b_ctx *ctx, size_t outlen,
+				    const void *key, size_t keylen)
+{
+	WARN_ON(IS_ENABLED(DEBUG) && (!outlen || outlen > BLAKE2B_HASH_SIZE ||
+		!key || !keylen || keylen > BLAKE2B_KEY_SIZE));
+
+	__blake2b_init(ctx, outlen, key, keylen);
+}
+
+/**
+ * blake2b_update() - Update a BLAKE2b context with message data
+ * @ctx: the context to update; must have been initialized
+ * @in: the message data
+ * @inlen: the data length in bytes
+ *
+ * This can be called any number of times.
+ *
+ * Context: Any context.
+ */
+void blake2b_update(struct blake2b_ctx *ctx, const u8 *in, size_t inlen);
+
+/**
+ * blake2b_final() - Finish computing a BLAKE2b hash
+ * @ctx: the context to finalize; must have been initialized
+ * @out: (output) the resulting BLAKE2b hash.  Its length will be equal to the
+ *	 @outlen that was passed to blake2b_init() or blake2b_init_key().
+ *
+ * After finishing, this zeroizes @ctx.  So the caller does not need to do it.
+ *
+ * Context: Any context.
+ */
+void blake2b_final(struct blake2b_ctx *ctx, u8 *out);
+
+/**
+ * blake2b() - Compute BLAKE2b hash in one shot
+ * @key: the key, or NULL for an unkeyed hash
+ * @keylen: the key length in bytes (at most BLAKE2B_KEY_SIZE), or 0 for an
+ *	    unkeyed hash
+ * @in: the message data
+ * @inlen: the data length in bytes
+ * @out: (output) the resulting BLAKE2b hash, with length @outlen
+ * @outlen: length of output hash value in bytes, at most BLAKE2B_HASH_SIZE
+ *
+ * Context: Any context.
+ */
+static inline void blake2b(const u8 *key, size_t keylen,
+			   const u8 *in, size_t inlen,
+			   u8 *out, size_t outlen)
+{
+	struct blake2b_ctx ctx;
+
+	WARN_ON(IS_ENABLED(DEBUG) && ((!in && inlen > 0) || !out || !outlen ||
+		outlen > BLAKE2B_HASH_SIZE || keylen > BLAKE2B_KEY_SIZE ||
+		(!key && keylen)));
+
+	__blake2b_init(&ctx, outlen, key, keylen);
+	blake2b_update(&ctx, in, inlen);
+	blake2b_final(&ctx, out);
+}
+
+#endif /* _CRYPTO_BLAKE2B_H */