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, 323 insertions, 0 deletions

diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S
new file mode 100644
index 000000000..ab087406d
--- /dev/null
+++ b/arch/mips/lib/memset.S
@@ -0,0 +1,323 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 1998, 1999, 2000 by Ralf Baechle
+ * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
+ * Copyright (C) 2007 by Maciej W. Rozycki
+ * Copyright (C) 2011, 2012 MIPS Technologies, Inc.
+ */
+#include <linux/export.h>
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
+#include <asm/regdef.h>
+
+#if LONGSIZE == 4
+#define LONG_S_L swl
+#define LONG_S_R swr
+#else
+#define LONG_S_L sdl
+#define LONG_S_R sdr
+#endif
+
+#ifdef CONFIG_CPU_MICROMIPS
+#define STORSIZE (LONGSIZE * 2)
+#define STORMASK (STORSIZE - 1)
+#define FILL64RG t8
+#define FILLPTRG t7
+#undef  LONG_S
+#define LONG_S LONG_SP
+#else
+#define STORSIZE LONGSIZE
+#define STORMASK LONGMASK
+#define FILL64RG a1
+#define FILLPTRG t0
+#endif
+
+#define LEGACY_MODE 1
+#define EVA_MODE    2
+
+/*
+ * No need to protect it with EVA #ifdefery. The generated block of code
+ * will never be assembled if EVA is not enabled.
+ */
+#define __EVAFY(insn, reg, addr) __BUILD_EVA_INSN(insn##e, reg, addr)
+#define ___BUILD_EVA_INSN(insn, reg, addr) __EVAFY(insn, reg, addr)
+
+#define EX(insn,reg,addr,handler)			\
+	.if \mode == LEGACY_MODE;			\
+9:		insn	reg, addr;			\
+	.else;						\
+9:		___BUILD_EVA_INSN(insn, reg, addr);	\
+	.endif;						\
+	.section __ex_table,"a";			\
+	PTR_WD	9b, handler;				\
+	.previous
+
+	.macro	f_fill64 dst, offset, val, fixup, mode
+	EX(LONG_S, \val, (\offset +  0 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset +  1 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset +  2 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset +  3 * STORSIZE)(\dst), \fixup)
+#if ((defined(CONFIG_CPU_MICROMIPS) && (LONGSIZE == 4)) || !defined(CONFIG_CPU_MICROMIPS))
+	EX(LONG_S, \val, (\offset +  4 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset +  5 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset +  6 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset +  7 * STORSIZE)(\dst), \fixup)
+#endif
+#if (!defined(CONFIG_CPU_MICROMIPS) && (LONGSIZE == 4))
+	EX(LONG_S, \val, (\offset +  8 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset +  9 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset + 10 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset + 11 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset + 12 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset + 13 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset + 14 * STORSIZE)(\dst), \fixup)
+	EX(LONG_S, \val, (\offset + 15 * STORSIZE)(\dst), \fixup)
+#endif
+	.endm
+
+	.align	5
+
+	/*
+	 * Macro to generate the __bzero{,_user} symbol
+	 * Arguments:
+	 * mode: LEGACY_MODE or EVA_MODE
+	 */
+	.macro __BUILD_BZERO mode
+	/* Initialize __memset if this is the first time we call this macro */
+	.ifnotdef __memset
+	.set __memset, 1
+	.endif
+
+	sltiu		t0, a2, STORSIZE	/* very small region? */
+	.set		noreorder
+	bnez		t0, .Lsmall_memset\@
+	 andi		t0, a0, STORMASK	/* aligned? */
+	.set		reorder
+
+#ifdef CONFIG_CPU_MICROMIPS
+	move		t8, a1			/* used by 'swp' instruction */
+	move		t9, a1
+#endif
+	.set		noreorder
+#ifndef CONFIG_CPU_DADDI_WORKAROUNDS
+	beqz		t0, 1f
+	 PTR_SUBU	t0, STORSIZE		/* alignment in bytes */
+#else
+	.set		noat
+	li		AT, STORSIZE
+	beqz		t0, 1f
+	 PTR_SUBU	t0, AT			/* alignment in bytes */
+	.set		at
+#endif
+	.set		reorder
+
+#ifndef CONFIG_CPU_NO_LOAD_STORE_LR
+	R10KCBARRIER(0(ra))
+#ifdef __MIPSEB__
+	EX(LONG_S_L, a1, (a0), .Lfirst_fixup\@)	/* make word/dword aligned */
+#else
+	EX(LONG_S_R, a1, (a0), .Lfirst_fixup\@)	/* make word/dword aligned */
+#endif
+	PTR_SUBU	a0, t0			/* long align ptr */
+	PTR_ADDU	a2, t0			/* correct size */
+
+#else /* CONFIG_CPU_NO_LOAD_STORE_LR */
+#define STORE_BYTE(N)				\
+	EX(sb, a1, N(a0), .Lbyte_fixup\@);	\
+	.set		noreorder;		\
+	beqz		t0, 0f;			\
+	 PTR_ADDU	t0, 1;			\
+	.set		reorder;
+
+	PTR_ADDU	a2, t0			/* correct size */
+	PTR_ADDU	t0, 1
+	STORE_BYTE(0)
+	STORE_BYTE(1)
+#if LONGSIZE == 4
+	EX(sb, a1, 2(a0), .Lbyte_fixup\@)
+#else
+	STORE_BYTE(2)
+	STORE_BYTE(3)
+	STORE_BYTE(4)
+	STORE_BYTE(5)
+	EX(sb, a1, 6(a0), .Lbyte_fixup\@)
+#endif
+0:
+	ori		a0, STORMASK
+	xori		a0, STORMASK
+	PTR_ADDIU	a0, STORSIZE
+#endif /* CONFIG_CPU_NO_LOAD_STORE_LR */
+1:	ori		t1, a2, 0x3f		/* # of full blocks */
+	xori		t1, 0x3f
+	andi		t0, a2, 0x40-STORSIZE
+	beqz		t1, .Lmemset_partial\@	/* no block to fill */
+
+	PTR_ADDU	t1, a0			/* end address */
+1:	PTR_ADDIU	a0, 64
+	R10KCBARRIER(0(ra))
+	f_fill64 a0, -64, FILL64RG, .Lfwd_fixup\@, \mode
+	bne		t1, a0, 1b
+
+.Lmemset_partial\@:
+	R10KCBARRIER(0(ra))
+	PTR_LA		t1, 2f			/* where to start */
+#ifdef CONFIG_CPU_MICROMIPS
+	LONG_SRL	t7, t0, 1
+#endif
+#if LONGSIZE == 4
+	PTR_SUBU	t1, FILLPTRG
+#else
+	.set		noat
+	LONG_SRL	AT, FILLPTRG, 1
+	PTR_SUBU	t1, AT
+	.set		at
+#endif
+	PTR_ADDU	a0, t0			/* dest ptr */
+	jr		t1
+
+	/* ... but first do longs ... */
+	f_fill64 a0, -64, FILL64RG, .Lpartial_fixup\@, \mode
+2:	andi		a2, STORMASK		/* At most one long to go */
+
+	.set		noreorder
+	beqz		a2, 1f
+#ifndef CONFIG_CPU_NO_LOAD_STORE_LR
+	 PTR_ADDU	a0, a2			/* What's left */
+	.set		reorder
+	R10KCBARRIER(0(ra))
+#ifdef __MIPSEB__
+	EX(LONG_S_R, a1, -1(a0), .Llast_fixup\@)
+#else
+	EX(LONG_S_L, a1, -1(a0), .Llast_fixup\@)
+#endif
+#else /* CONFIG_CPU_NO_LOAD_STORE_LR */
+	 PTR_SUBU	t0, $0, a2
+	.set		reorder
+	move		a2, zero		/* No remaining longs */
+	PTR_ADDIU	t0, 1
+	STORE_BYTE(0)
+	STORE_BYTE(1)
+#if LONGSIZE == 4
+	EX(sb, a1, 2(a0), .Lbyte_fixup\@)
+#else
+	STORE_BYTE(2)
+	STORE_BYTE(3)
+	STORE_BYTE(4)
+	STORE_BYTE(5)
+	EX(sb, a1, 6(a0), .Lbyte_fixup\@)
+#endif
+0:
+#endif /* CONFIG_CPU_NO_LOAD_STORE_LR */
+1:	move		a2, zero
+	jr		ra
+
+.Lsmall_memset\@:
+	PTR_ADDU	t1, a0, a2
+	beqz		a2, 2f
+
+1:	PTR_ADDIU	a0, 1			/* fill bytewise */
+	R10KCBARRIER(0(ra))
+	.set		noreorder
+	bne		t1, a0, 1b
+	 EX(sb, a1, -1(a0), .Lsmall_fixup\@)
+	.set		reorder
+
+2:	move		a2, zero
+	jr		ra			/* done */
+	.if __memset == 1
+	END(memset)
+	.set __memset, 0
+	.endif
+
+#ifdef CONFIG_CPU_NO_LOAD_STORE_LR
+.Lbyte_fixup\@:
+	/*
+	 * unset_bytes = (#bytes - (#unaligned bytes)) - (-#unaligned bytes remaining + 1) + 1
+	 *      a2     =             a2                -              t0                   + 1
+	 */
+	PTR_SUBU	a2, t0
+	PTR_ADDIU	a2, 1
+	jr		ra
+#endif /* CONFIG_CPU_NO_LOAD_STORE_LR */
+
+.Lfirst_fixup\@:
+	/* unset_bytes already in a2 */
+	jr	ra
+
+.Lfwd_fixup\@:
+	/*
+	 * unset_bytes = partial_start_addr +  #bytes   -     fault_addr
+	 *      a2     =         t1         + (a2 & 3f) - $28->task->BUADDR
+	 */
+	PTR_L		t0, TI_TASK($28)
+	andi		a2, 0x3f
+	LONG_L		t0, THREAD_BUADDR(t0)
+	LONG_ADDU	a2, t1
+	LONG_SUBU	a2, t0
+	jr		ra
+
+.Lpartial_fixup\@:
+	/*
+	 * unset_bytes = partial_end_addr +      #bytes     -     fault_addr
+	 *      a2     =       a0         + (a2 & STORMASK) - $28->task->BUADDR
+	 */
+	PTR_L		t0, TI_TASK($28)
+	andi		a2, STORMASK
+	LONG_L		t0, THREAD_BUADDR(t0)
+	LONG_ADDU	a2, a0
+	LONG_SUBU	a2, t0
+	jr		ra
+
+.Llast_fixup\@:
+	/* unset_bytes already in a2 */
+	jr		ra
+
+.Lsmall_fixup\@:
+	/*
+	 * unset_bytes = end_addr - current_addr + 1
+	 *      a2     =    t1    -      a0      + 1
+	 */
+	PTR_SUBU	a2, t1, a0
+	PTR_ADDIU	a2, 1
+	jr		ra
+
+	.endm
+
+/*
+ * memset(void *s, int c, size_t n)
+ *
+ * a0: start of area to clear
+ * a1: char to fill with
+ * a2: size of area to clear
+ */
+
+LEAF(memset)
+EXPORT_SYMBOL(memset)
+	move		v0, a0			/* result */
+	beqz		a1, 1f
+
+	andi		a1, 0xff		/* spread fillword */
+	LONG_SLL		t1, a1, 8
+	or		a1, t1
+	LONG_SLL		t1, a1, 16
+#if LONGSIZE == 8
+	or		a1, t1
+	LONG_SLL		t1, a1, 32
+#endif
+	or		a1, t1
+1:
+#ifndef CONFIG_EVA
+FEXPORT(__bzero)
+EXPORT_SYMBOL(__bzero)
+#endif
+	__BUILD_BZERO LEGACY_MODE
+
+#ifdef CONFIG_EVA
+LEAF(__bzero)
+EXPORT_SYMBOL(__bzero)
+	__BUILD_BZERO EVA_MODE
+END(__bzero)
+#endif