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

From: Borislav Petkov <bp@alien8.de>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: "Dr. Greg" <greg@enjellic.com>,
	"Daniel P. Berrang??" <berrange@redhat.com>,
	"Reshetova, Elena" <elena.reshetova@intel.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"x86@kernel.org" <x86@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
	Kuppuswamy Sathyanarayanan
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	"Nakajima, Jun" <jun.nakajima@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"Kalra, Ashish" <ashish.kalra@amd.com>,
	Sean Christopherson <seanjc@google.com>,
	"linux-coco@lists.linux.dev" <linux-coco@lists.linux.dev>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] x86/random: Issue a warning if RDRAND or RDSEED fails
Date: Fri, 9 Feb 2024 22:45:30 +0100	[thread overview]
Message-ID: <20240209214530.GHZcac-vOym8k3IuJm@fat_crate.local> (raw)
In-Reply-To: <CAHmME9pEVNM6UVW+pKbTZEhsnrGvq5ERMOSC1ezdrCn96q36kA@mail.gmail.com>

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