| Message ID | 20220410214951.55294-9-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | archs/random: fallback to using ktime_read_raw_clock() if no cycle counter | expand |
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h index 01a300a9700b..dad3027bf6a2 100644 --- a/arch/x86/include/asm/tsc.h +++ b/arch/x86/include/asm/tsc.h @@ -28,6 +28,16 @@ static inline cycles_t get_cycles(void) return rdtsc(); } +static inline unsigned long random_get_entropy(void) +{ +#ifndef CONFIG_X86_TSC + if (!boot_cpu_has(X86_FEATURE_TSC)) + return ktime_read_raw_clock(); +#endif + return rdtsc(); +} +#define random_get_entropy random_get_entropy + extern struct system_counterval_t convert_art_to_tsc(u64 art); extern struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns);
In the event that random_get_entropy() can't access a cycle counter or similar, falling back to returning 0 is really not the best we can do. Instead, at least calling ktime_read_raw_clock() would be preferable, because that always needs to return _something_, even falling back to jiffies eventually. It's not as though ktime_read_raw_clock() is super high precision or guaranteed to be entropic, but basically anything that's not zero all the time is better than returning zero all the time. If CONFIG_X86_TSC=n, then it's possible that we're running on a 486 with no RDTSC, so we only need the fallback code for that case. Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: x86@kernel.org Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- arch/x86/include/asm/tsc.h | 10 ++++++++++ 1 file changed, 10 insertions(+)