Commits
Len Brown committed 0007bccc3cf
x86: Replace RDRAND forced-reseed with simple sanity check x86_init_rdrand() was added with 2 goals: 1. Sanity check that the built-in-self-test circuit on the Digital Random Number Generator (DRNG) is not complaining. As RDRAND HW self-checks on every invocation, this goal is achieved by simply invoking RDRAND and checking its return code. 2. Force a full re-seed of the random number generator. This was done out of paranoia to benefit the most un-sophisticated DRNG implementation conceivable in the architecture, an implementation that does not exist, and unlikely ever will. This worst-case full-re-seed is achieved by invoking a 64-bit RDRAND 8192 times. Unfortunately, this worst-case re-seed costs O(1,000us). Magnifying this cost, it is done from identify_cpu(), which is the synchronous critical path to bring a processor on-line -- repeated for every logical processor in the system at boot and resume from S3. As it is very expensive, and of highly dubious value, we delete the worst-case re-seed from the kernel. We keep the 1st goal -- sanity check the hardware, and mark it absent if it complains. This change reduces the cost of x86_init_rdrand() by a factor of 1,000x, to O(1us) from O(1,000us). Signed-off-by: Len Brown <len.brown@intel.com> Link: http://lkml.kernel.org/r/058618cc56ec6611171427ad7205e37e377aa8d4.1439738240.git.len.brown@intel.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>