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time/sched_clock: Provide sched_clock_noinstr()

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With the intent to provide local_clock_noinstr(), a variant of
local_clock() that's safe to be called from noinstr code (with the
assumption that any such code will already be non-preemptible),
prepare for things by providing a noinstr sched_clock_noinstr() function.

Specifically, preempt_enable_*() calls out to schedule(), which upsets
noinstr validation efforts.

As such, pull out the preempt_{dis,en}able_notrace() requirements from
the sched_clock_read() implementations by explicitly providing it in
the sched_clock() function.

This further requires said sched_clock_read() functions to be noinstr
themselves, for ARCH_WANTS_NO_INSTR users. See the next few patches.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com>  # Hyper-V
Link: https://lore.kernel.org/r/20230519102715.302350330@infradead.org
This commit is contained in:
Peter Zijlstra 2023-05-19 12:21:00 +02:00
parent d16317de9b
commit 5949a68c73
1 changed files with 16 additions and 6 deletions
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22
kernel/time/sched_clock.c
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@ -64,7 +64,7 @@ static struct clock_data cd ____cacheline_aligned = {
.actual_read_sched_clock = jiffy_sched_clock_read,
};
static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
static __always_inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
{
return (cyc * mult) >> shift;
}
@ -80,23 +80,33 @@ notrace int sched_clock_read_retry(unsigned int seq)
return raw_read_seqcount_latch_retry(&cd.seq, seq);
}
unsigned long long notrace sched_clock(void)
unsigned long long noinstr sched_clock_noinstr(void)
{
u64 cyc, res;
unsigned int seq;
struct clock_read_data *rd;
unsigned int seq;
u64 cyc, res;
do {
rd = sched_clock_read_begin(&seq);
seq = raw_read_seqcount_latch(&cd.seq);
rd = cd.read_data + (seq & 1);
cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
rd->sched_clock_mask;
res = rd->epoch_ns + cyc_to_ns(cyc, rd->mult, rd->shift);
} while (sched_clock_read_retry(seq));
} while (raw_read_seqcount_latch_retry(&cd.seq, seq));
return res;
}
unsigned long long notrace sched_clock(void)
{
unsigned long long ns;
preempt_disable_notrace();
ns = sched_clock_noinstr();
preempt_enable_notrace();
return ns;
}
/*
* Updating the data required to read the clock.
*