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Date: Tue, 6 Feb 2024 08:04:57 +0000
From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= <berrange@redhat.com>
To: "Dr. Greg" <greg@enjellic.com>
Cc: "Reshetova, Elena" <elena.reshetova@intel.com>,
	"Jason A. Donenfeld" <Jason@zx2c4.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>, Borislav Petkov <bp@alien8.de>,
	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
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Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= <berrange@redhat.com>
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User-Agent: Mutt/2.2.12 (2023-09-09)

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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