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

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Date: Tue, 30 Jan 2024 10:15:35 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Dave Hansen <dave.hansen@...el.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>
CC: "Reshetova, Elena" <elena.reshetova@...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>,
        "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 January 30, 2024 9:58:09 AM PST, Dave Hansen <dave.hansen@...el.com> wrote:
>On 1/30/24 09:49, Jason A. Donenfeld wrote:
>>> Anybody disagree?
>> Yes, I disagree. I made a trivial test that shows RDSEED breaks easily
>> in a busy loop. So at the very least, your statement holds true only
>> for RDRAND.
>
>Well, darn. :)
>
>Any chance you could share some more information about the environment
>where you're seeing this?  It'd be good to reconcile what you're seeing
>with how the hardware is expected to behave.

What CPU is this and could you clarify exactly how you run your busy loop?