| Message ID | 20220426083301.816458-1-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | None | expand |
On Tue, Apr 26 2022 at 10:33, Jason A. Donenfeld wrote: Subject: x86/tsc: Use ..... This has absolutely nothing to do with ASM and the sentence after the colon starts with an uppercase letter. > In the event that random_get_entropy() can't access a cycle counter or > similar, falling back to returning 0 is suboptimal. Instead, fallback > to calling random_get_entropy_fallback(), which isn't extremely high > precision or guaranteed to be entropic, but is certainly better than > returning zero all the time. > > If CONFIG_X86_TSC=n, then it's possible for the kernel to run on systems > without RDTSC, such as 486 and certain 586, so the fallback code is only > required for that case. > > As well, fix up both the new function and the get_cycles() function from > which it was derived to use cpu_feature_enabled() rather than > boot_cpu_has(), and use !IS_ENABLED() instead of #ifndef. > > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Borislav Petkov <bp@alien8.de> > Cc: x86@kernel.org Same comments vs. Cc's > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > --- > Changes v6->v7: > - Adjust commit subject and body to match tip commit style. Mostly ... :) With that fixed: Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/include/asm/timex.h b/arch/x86/include/asm/timex.h index a4a8b1b16c0c..956e4145311b 100644 --- a/arch/x86/include/asm/timex.h +++ b/arch/x86/include/asm/timex.h @@ -5,6 +5,15 @@ #include <asm/processor.h> #include <asm/tsc.h> +static inline unsigned long random_get_entropy(void) +{ + if (!IS_ENABLED(CONFIG_X86_TSC) && + !cpu_feature_enabled(X86_FEATURE_TSC)) + return random_get_entropy_fallback(); + return rdtsc(); +} +#define random_get_entropy random_get_entropy + /* Assume we use the PIT time source for the clock tick */ #define CLOCK_TICK_RATE PIT_TICK_RATE diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h index 01a300a9700b..fbdc3d951494 100644 --- a/arch/x86/include/asm/tsc.h +++ b/arch/x86/include/asm/tsc.h @@ -20,13 +20,12 @@ extern void disable_TSC(void); static inline cycles_t get_cycles(void) { -#ifndef CONFIG_X86_TSC - if (!boot_cpu_has(X86_FEATURE_TSC)) + if (!IS_ENABLED(CONFIG_X86_TSC) && + !cpu_feature_enabled(X86_FEATURE_TSC)) return 0; -#endif - return rdtsc(); } +#define get_cycles get_cycles 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 suboptimal. Instead, fallback to calling random_get_entropy_fallback(), which isn't extremely high precision or guaranteed to be entropic, but is certainly better than returning zero all the time. If CONFIG_X86_TSC=n, then it's possible for the kernel to run on systems without RDTSC, such as 486 and certain 586, so the fallback code is only required for that case. As well, fix up both the new function and the get_cycles() function from which it was derived to use cpu_feature_enabled() rather than boot_cpu_has(), and use !IS_ENABLED() instead of #ifndef. Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: x86@kernel.org Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- Changes v6->v7: - Adjust commit subject and body to match tip commit style. - Use !IS_ENABLED() instead of #ifndef. arch/x86/include/asm/timex.h | 9 +++++++++ arch/x86/include/asm/tsc.h | 7 +++---- 2 files changed, 12 insertions(+), 4 deletions(-)