This patch hardens the implementation of hpet clock with 64-bit counter
by enforcing that every read of the main counter is NOT less than
the previous value.
Fixes #382
Signed-off-by: Waldemar Kozaczuk <jwkozac...@gmail.com>
---
drivers/hpet.cc | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/drivers/hpet.cc b/drivers/hpet.cc
index 22afae7d..ba9ed3bc 100644
--- a/drivers/hpet.cc
+++ b/drivers/hpet.cc
@@ -29,6 +29,7 @@ protected:
mmioaddr_t _addr;
uint64_t _wall;
uint64_t _period;
+ std::atomic<s64> _last_read_counter;
};
#define HPET_COUNTER 0x0f0
@@ -55,11 +56,23 @@ public:
hpet_64bit_clock(mmioaddr_t hpet_mmio_address) :
hpetclock(hpet_mmio_address) {}
protected:
virtual s64 time() override __attribute__((no_instrument_function)) {
- return _wall + mmio_getq(_addr + HPET_COUNTER) * _period;;
+ return _wall + fetch_counter() * _period;
}
virtual s64 uptime() override __attribute__((no_instrument_function)) {
- return mmio_getq(_addr + HPET_COUNTER) * _period;;
+ return fetch_counter() * _period;
+ }
+private:
+ s64 fetch_counter() {
+ auto last_valid_counter = _last_read_counter.load();
+
+ s64 counter;
+ do {
+ counter = mmio_getq(_addr + HPET_COUNTER);
+ } while (counter < last_valid_counter);
+
+ _last_read_counter.store(counter);
+ return counter;
}
};
@@ -99,6 +112,7 @@ hpetclock::hpetclock(mmioaddr_t hpet_mmio_address)
mmio_setl(_addr + HPET_COUNTER, 0);
mmio_setl(_addr + HPET_COUNTER + 4, 0);
+ _last_read_counter.store(0);
_wall = r->wallclock_ns();
// We got them all, now we restart the HPET.
--
2.20.1
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