linux-kernel - Re: [PATCH v2] x86/amd: Disable RDSEED on AMD Zen5 because of an error.

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Message-ID: <aQ57ofElS-N0gEco@zx2c4.com>
Date: Sat, 8 Nov 2025 00:07:13 +0100
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Thiago Macieira <thiago.macieira@...el.com>
Cc: Borislav Petkov <bp@...en8.de>, Christopher Snowhill <chris@...e54.net>,
	Gregory Price <gourry@...rry.net>, x86@...nel.org,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	dave.hansen@...ux.intel.com, hpa@...or.com, peterz@...radead.org,
	mario.limonciello@....com, riel@...riel.com, yazen.ghannam@....com,
	me@...aill.net, kai.huang@...el.com, sandipan.das@....com,
	darwi@...utronix.de, stable@...r.kernel.org
Subject: Re: [PATCH v2] x86/amd: Disable RDSEED on AMD Zen5 because of an
 error.

Hi Thiago,

On Fri, Nov 07, 2025 at 11:55:35AM -0800, Thiago Macieira wrote:
> I'm not asking about the performance of generating new random numbers in this 
> process.
> 
> I am asking about the system-wide impact that draining the entropy source 
> would have. Is that a bad thing?
> 
> I suspect the answer is "no" because it's the same as /dev/urandom anyway.

Oh. "Entropy source draining" is not a real thing. There used to be
bizarre behavior related to /dev/random (not urandom), but this has been
gone for ages. And even the non-getrandom Linux fallback code uses
/dev/urandom before /dev/random. So not even on old kernels is this an
issue. You can keep generating random numbers forever without worrying
about running out of juice or irritating other processes.

Jason