| Message ID | 20220412172754.149498-8-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | archs/random: fallback to best raw ktime when no cycle counter | expand |
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h index 01a300a9700b..194dc1e3f77c 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 random_get_entropy_fallback(); +#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 random_get_entropy_fallback() would be preferable, because that always needs to return _something_, even falling back to jiffies eventually. It's not as though random_get_entropy_fallback() 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(+)