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

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Date: Tue, 6 Feb 2024 13:50:50 +0000
From: Daniel P. Berrangé <berrange@...hat.com>
To: "Dr. Greg" <greg@...ellic.com>
Cc: "Reshetova, Elena" <elena.reshetova@...el.com>,
	"Jason A. Donenfeld" <Jason@...c4.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>, Borislav Petkov <bp@...en8.de>,
	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 Tue, Feb 06, 2024 at 06:04:45AM -0600, Dr. Greg wrote:
> On Tue, Feb 06, 2024 at 08:04:57AM +0000, Daniel P. Berrang?? wrote:
> 
> Good morning to everyone.
> 
> > On Mon, Feb 05, 2024 at 07:12:47PM -0600, Dr. Greg wrote:
> > > 
> > > Actually, I now believe there is clear evidence that the problem is
> > > indeed Intel specific.  In light of our testing, it will be
> > > interesting to see what your 'AR' returns with respect to an official
> > > response from Intel engineering on this issue.
> > > 
> > > One of the very bright young engineers collaborating on Quixote, who
> > > has been following this conversation, took it upon himself to do some
> > > very methodical engineering analysis on this issue.  I'm the messenger
> > > but this is very much his work product.
> > > 
> > > Executive summary is as follows:
> > > 
> > > - No RDRAND depletion failures were observable with either the Intel
> > >   or AMD hardware that was load tested.
> > > 
> > > - RDSEED depletion is an Intel specific issue, AMD's RDSEED
> > >   implementation could not be provoked into failure.
> 
> > My colleague ran a multithread parallel stress test program on his
> > 16core/2HT AMD Ryzen (Zen4 uarch) and saw a 80% failure rate in
> > RDSEED.
> 
> Interesting datapoint, thanks for forwarding it along, so the issue
> shows up on at least some AMD platforms as well.

I got access to a couple more AMD machines. An EPYC 24core/2HT
(Zen-1 uarch) and an EPYC 2socket/16core/2HT (Zen-3 uarch).

Both of these show 100% success with RDSEED. So there's clearly
some variance across AMD SKUs. So perhaps this is an EPYC vs Ryzen
distinction, with the server focused EPYCs able to sustain RDSEED.


With regards,
Daniel
-- 
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