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sched_ext: Add scx_arena_to_kaddr() / scx_kaddr_to_arena()

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Translating between a BPF-arena pointer and its kernel-side address is just
an add or subtract of the arena's kern_vm start. More such translations are
coming, so cache that start on scx_sched as @arena_kern_base at arena attach
and wrap both directions. Convert the existing open-coded subtraction in
scx_call_op_set_cpumask().

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo
2026-06-03 23:57:03 -10:00
parent 70390da50c
commit 2e05f2fd0d
2 changed files with 40 additions and 15 deletions
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19
kernel/sched/ext.c
View File

@@ -622,19 +622,13 @@ static inline void scx_call_op_set_cpumask(struct scx_sched *sch, struct rq *rq,
if (scx_is_cid_type()) {
struct scx_cmask *kern_va = *this_cpu_ptr(sch->set_cmask_scratch);
unsigned long uaddr = (unsigned long)kern_va;
/* arena.o, which defines these, is built only on MMU && 64BIT */
#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
uaddr -= bpf_arena_map_kern_vm_start(sch->arena_map);
#endif
/*
* Build the per-CPU arena cmask and hand BPF the uaddr. Caller
* holds the rq lock with IRQs disabled, which makes us the sole
* user of the scratch area.
* Build the per-CPU arena cmask and hand BPF its arena address.
* Caller holds the rq lock with IRQs disabled, which makes us
* the sole user of the scratch area.
*/
scx_cpumask_to_cmask(cpumask, kern_va);
sch->ops_cid.set_cmask(task, (struct scx_cmask *)uaddr);
sch->ops_cid.set_cmask(task, scx_kaddr_to_arena(sch, kern_va));
} else {
sch->ops.set_cpumask(task, cpumask);
}
@@ -6977,6 +6971,11 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
* runs through scx_sched_free_rcu_work() which puts it.
*/
sch->arena_map = cmd->arena_map;
/* BPF arena is only available on MMU && 64BIT */
#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
if (sch->arena_map)
sch->arena_kern_base = bpf_arena_map_kern_vm_start(sch->arena_map);
#endif
cmd->arena_map = NULL;
return sch;

36
kernel/sched/ext_internal.h
View File

@@ -1118,17 +1118,18 @@ struct scx_sched {
* progs. NULL on cpu-form.
*
* @arena_pool sub-allocates @arena_map. Each gen_pool chunk is added
* at the kernel-side mapping address. Grows on demand and pages are
* not released until sched destroy.
* at the kernel-side mapping address. @arena_kern_base is the start
* of the arena's kern_vm range. See scx_arena_to_kaddr() and
* scx_kaddr_to_arena().
*/
struct bpf_map *arena_map;
struct gen_pool *arena_pool;
uintptr_t arena_kern_base;
/*
* Per-CPU arena cmask used by scx_call_op_set_cpumask() to hand a cmask
* to ops_cid.set_cmask(). The kernel writes through the stored kern_va;
* the BPF-arena uaddr handed to BPF is recovered by subtracting the
* arena's kern_vm_start.
* to ops_cid.set_cmask(). The kernel writes through the stored kern_va
* and hands BPF its arena pointer via scx_kaddr_to_arena().
*/
struct scx_cmask * __percpu *set_cmask_scratch;
@@ -1205,6 +1206,31 @@ struct scx_sched {
struct scx_sched *ancestors[];
};
/**
* scx_arena_to_kaddr - Translate a BPF-arena pointer to its kernel address
* @sch: scheduler whose arena hosts @bpf_ptr
* @bpf_ptr: BPF-arena pointer, only the low 32 bits are used
*
* The (u32) cast normalizes any input into the arena's 4 GiB kern_vm range,
* which combined with scratch-page fault recovery makes the returned pointer
* safe to dereference up to GUARD_SZ / 2 past the intended object. Accesses
* larger than GUARD_SZ / 2 must be explicitly bounds-checked.
*/
static inline void *scx_arena_to_kaddr(struct scx_sched *sch, const void *bpf_ptr)
{
return (void *)(sch->arena_kern_base + (u32)(uintptr_t)bpf_ptr);
}
/**
* scx_kaddr_to_arena - Translate a kernel arena address to its BPF form
* @sch: scheduler whose arena hosts @kaddr
* @kaddr: kernel-side arena address, supplied by trusted kernel code
*/
static inline void *scx_kaddr_to_arena(struct scx_sched *sch, const void *kaddr)
{
return (void *)((uintptr_t)kaddr - sch->arena_kern_base);
}
enum scx_wake_flags {
/* expose select WF_* flags as enums */
SCX_WAKE_FORK = WF_FORK,