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random: remove batched entropy locking

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Rather than use spinlocks to protect batched entropy, we can instead
disable interrupts locally, since we're dealing with per-cpu data, and
manage resets with a basic generation counter. At the same time, we
can't quite do this on PREEMPT_RT, where we still want spinlocks-as-
mutexes semantics. So we use a local_lock_t, which provides the right
behavior for each. Because this is a per-cpu lock, that generation
counter is still doing the necessary CPU-to-CPU communication.

This should improve performance a bit. It will also fix the linked splat
that Jonathan received with a PROVE_RAW_LOCK_NESTING=y.

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Reported-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Tested-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/lkml/YfMa0QgsjCVdRAvJ@latitude/
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld 2022-01-28 23:29:45 +01:00
parent 5d58ea3a31
commit 77760fd7f7
1 changed files with 28 additions and 27 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

55
drivers/char/random.c
View file

@ -1731,13 +1731,16 @@ static int __init random_sysctls_init(void)
device_initcall(random_sysctls_init);
#endif /* CONFIG_SYSCTL */
static atomic_t batch_generation = ATOMIC_INIT(0);
struct batched_entropy {
union {
u64 entropy_u64[CHACHA_BLOCK_SIZE / sizeof(u64)];
u32 entropy_u32[CHACHA_BLOCK_SIZE / sizeof(u32)];
};
local_lock_t lock;
unsigned int position;
spinlock_t batch_lock;
int generation;
};
/*
@ -1749,7 +1752,7 @@ struct batched_entropy {
* point prior.
*/
static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = {
.batch_lock = __SPIN_LOCK_UNLOCKED(batched_entropy_u64.lock),
.lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock)
};
u64 get_random_u64(void)
@ -1758,67 +1761,65 @@ u64 get_random_u64(void)
unsigned long flags;
struct batched_entropy *batch;
static void *previous;
int next_gen;
warn_unseeded_randomness(&previous);
local_lock_irqsave(&batched_entropy_u64.lock, flags);
batch = raw_cpu_ptr(&batched_entropy_u64);
spin_lock_irqsave(&batch->batch_lock, flags);
if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
next_gen = atomic_read(&batch_generation);
if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0 ||
next_gen != batch->generation) {
extract_crng((u8 *)batch->entropy_u64);
batch->position = 0;
batch->generation = next_gen;
}
ret = batch->entropy_u64[batch->position++];
spin_unlock_irqrestore(&batch->batch_lock, flags);
local_unlock_irqrestore(&batched_entropy_u64.lock, flags);
return ret;
}
EXPORT_SYMBOL(get_random_u64);
static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = {
.batch_lock = __SPIN_LOCK_UNLOCKED(batched_entropy_u32.lock),
.lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock)
};
u32 get_random_u32(void)
{
u32 ret;
unsigned long flags;
struct batched_entropy *batch;
static void *previous;
int next_gen;
warn_unseeded_randomness(&previous);
local_lock_irqsave(&batched_entropy_u32.lock, flags);
batch = raw_cpu_ptr(&batched_entropy_u32);
spin_lock_irqsave(&batch->batch_lock, flags);
if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) {
next_gen = atomic_read(&batch_generation);
if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0 ||
next_gen != batch->generation) {
extract_crng((u8 *)batch->entropy_u32);
batch->position = 0;
batch->generation = next_gen;
}
ret = batch->entropy_u32[batch->position++];
spin_unlock_irqrestore(&batch->batch_lock, flags);
local_unlock_irqrestore(&batched_entropy_u32.lock, flags);
return ret;
}
EXPORT_SYMBOL(get_random_u32);
/* It's important to invalidate all potential batched entropy that might
* be stored before the crng is initialized, which we can do lazily by
* simply resetting the counter to zero so that it's re-extracted on the
* next usage. */
* bumping the generation counter.
*/
static void invalidate_batched_entropy(void)
{
int cpu;
unsigned long flags;
for_each_possible_cpu(cpu) {
struct batched_entropy *batched_entropy;
batched_entropy = per_cpu_ptr(&batched_entropy_u32, cpu);
spin_lock_irqsave(&batched_entropy->batch_lock, flags);
batched_entropy->position = 0;
spin_unlock(&batched_entropy->batch_lock);
batched_entropy = per_cpu_ptr(&batched_entropy_u64, cpu);
spin_lock(&batched_entropy->batch_lock);
batched_entropy->position = 0;
spin_unlock_irqrestore(&batched_entropy->batch_lock, flags);
}
atomic_inc(&batch_generation);
}
/**