Re: [GIT pull] x86/urgent for 5.3-rc5

From: Linus Torvalds
Date: Sun Aug 25 2019 - 13:18:40 EST

On Sun, Aug 25, 2019 at 2:45 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> - Clear the RDRAND CPUID bit on AMD family 15h and 16h CPUs which are
> affected by broken firmware which does not initialize RDRAND correctly
> after resume. Add a command line parameter to override this for machine
> which either do not use suspend/resume or have a fixed
> BIOS. Unfortunately there is no way to detect this on boot, so the only
> safe decision is to turn it off by default.

Not doing the Zen 2 boot-time case? Everybody assumes that all
firmware has been fixed?

That one should be easy to verify since it happens at boot: just do
"rdrand" twice, and if it returns all-ones both times, it's broken.