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

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Message-ID: <ZcHoKUElwXGPzrWb@redhat.com>
Date: Tue, 6 Feb 2024 08:04:57 +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 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.

> - AMD's RDRAND/RDSEED implementation is significantly slower than
>   Intel's.

Yes, we also noticed the AMD impl is horribly slow compared to Intel,
had to cut test iterations x100

With regards,
Daniel
-- 
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