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

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Message-ID: <aQ5E2ArhkmziwWA8@zx2c4.com>
Date: Fri, 7 Nov 2025 20:13:28 +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.

On Wed, Nov 05, 2025 at 08:41:01AM -0800, Thiago Macieira wrote:
> > Oh yea, good question. Well, with every major OS now having a mechanism
> > to skip syscalls for random numbers, I guess you could indeed just alias
> > global() to system() and call it a day. Then users really cannot shoot
> > themselves in the foot. That would be simpler too. Seems like the best
> > option.
> 
> Indeed.
> 
> But consider people who haven't upgraded Linux (yes, we get people asking to 
> keep everything intact in their system, but upgrade Qt only, then complain 
> when our dependency minimums change). How much of an impact would they have?

I suppose you could benchmark it and see if it matters. The syscall is
obviously slower than the megafast vDSO code, so it will probably also
be a bit slower than the MT code. But I suspect for most use cases maybe
it doesn't matter that much? It's worth a try and seeing if anybody
complains.

Jason