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

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Date: Fri, 9 Feb 2024 22:45:30 +0100
From: Borislav Petkov <bp@...en8.de>
To: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: "Dr. Greg" <greg@...ellic.com>,
	"Daniel P. Berrang??" <berrange@...hat.com>,
	"Reshetova, Elena" <elena.reshetova@...el.com>,
	"Hansen, Dave" <dave.hansen@...el.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.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 Fri, Feb 09, 2024 at 08:49:40PM +0100, Jason A. Donenfeld wrote:
> While you're here,

I was here the whole time, lurking in the shadows. :)

> Is it actually possible to make RDRAND usage "fair" between different
> security contexts? Or am I totally delusional and this is not how the
> hardware works or can ever work?

Yeah, I know exactly what you mean and I won't go into details for
obvious reasons. Two things:

* Starting with Zen3, provided properly configured hw RDRAND will never
fail. It is also fair when feeding the different contexts.

* My hardware engineers tell me that this is tough to do for RDSEED

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette