linux-kernel - Re: [PATCH 2/2] x86/random: Issue a warning if RDRAND or RDSEED fails

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Date: Tue, 30 Jan 2024 19:23:23 +0100
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Dave Hansen <dave.hansen@...el.com>, "Reshetova, Elena" <elena.reshetova@...el.com>, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "x86@...nel.org" <x86@...nel.org>, 
	"Theodore Ts'o" <tytso@....edu>, 
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>, 
	"Nakajima, Jun" <jun.nakajima@...el.com>, Tom Lendacky <thomas.lendacky@....com>, 
	"Kalra, Ashish" <ashish.kalra@....com>, Sean Christopherson <seanjc@...gle.com>, 
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86/random: Issue a warning if RDRAND or RDSEED fails

On Tue, Jan 30, 2024 at 7:16 PM H. Peter Anvin <hpa@...or.com> wrote:
>
> On January 30, 2024 9:58:09 AM PST, Dave Hansen <dave.hansen@...el.com> wrote:
> >On 1/30/24 09:49, Jason A. Donenfeld wrote:
> >>> Anybody disagree?
> >> Yes, I disagree. I made a trivial test that shows RDSEED breaks easily
> >> in a busy loop. So at the very least, your statement holds true only
> >> for RDRAND.
> >
> >Well, darn. :)
> >
> >Any chance you could share some more information about the environment
> >where you're seeing this?  It'd be good to reconcile what you're seeing
> >with how the hardware is expected to behave.
>
> What CPU is this and could you clarify exactly how you run your busy loop?

That is already in this thread already. Maybe catch up on the whole
thing and then jump back in?
https://lore.kernel.org/all/Zbjw5hRHr_E6k18r@zx2c4.com/