From: "Jason A. Donenfeld" Jason@zx2c4.com
stable inclusion from stable-v5.10.119 commit 25d4fdf1f0f85e81e71d7c7e6cbcceb37d2ef65a category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6BB
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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commit 3bd4abc07a267e6a8b33d7f8717136e18f921c53 upstream.
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.
Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Reviewed-by: Thomas Gleixner tglx@linutronix.de 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com Acked-by: Xie XiuQi xiexiuqi@huawei.com --- arch/x86/include/asm/timex.h | 9 +++++++++ arch/x86/include/asm/tsc.h | 7 +++---- 2 files changed, 12 insertions(+), 4 deletions(-)
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);