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From: Borislav Petkov <>
To: "Lendacky, Thomas" <>
Cc: "" <>,
	"" <>,
	"" <>,
	"" <>,
	Thomas Gleixner <>,
	Ingo Molnar <>,
	"Rafael J . Wysocki" <>,
	Pavel Machek <>, Chen Yu <>,
	Jonathan Corbet <>
Subject: Re: [PATCH] x86/CPU/AMD: Clear RDRAND CPUID bit on AMD family 15h/16h
Date: Thu, 15 Aug 2019 17:34:47 +0200	[thread overview]
Message-ID: <20190815153447.GH15313@zn.tnic> (raw)
In-Reply-To: <>

On Thu, Aug 15, 2019 at 01:47:24PM +0000, Lendacky, Thomas wrote:
> Sure, I can do that. Do we want to tie this into the nordrand option and
> add rdrand=off or keep that separate?

Yeah, I was looking at that this morning and I'd say keep 'em separate
because if you have to tie, you need to export functions and then


in the nordrand callback but then F15h and F16h don't have RDSEED and
people would wonder, why clear RDSEED on AMD, blabla... so keeping them
separate saves us all that.

> I think this is a clearer indication that the action has taken place.

Yeah, but what does that bring us? You wanna know this now, while
testing. Once that whole effort is done, it is a useless printing of
info which you have in cpuinfo already.

> Not sure what you mean. We can't use the DMI stuff for this. So now, with
> the x86 family checks, if anyone adds some DMI stuff or x86 family stuff
> in the future that matches both the DMI and x86 family checks, this will
> be called more than once and so you need to copy any previous settings and
> add the new ones.

I had a suspicion that it was something like that. Ok, this is not a
big structure currently so I guess it is fine but if it keeps growing,
it would need a proper redesign like making it a list and callbacks
doing list_add_tail() for MSRs which get added. It would avoid that
kmalloc and copying which is silly. Please put a comment ontop why we're

> Except that X86_FEATURE_RDRAND isn't set anymore. I could create a new
> software feature that is set when the CPUID bit is cleared if that's
> preferred.

Nah, let's leave it like you had it.



Good mailing practices for 400: avoid top-posting and trim the reply.

  reply	other threads:[~2019-08-15 15:34 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-14 21:17 [PATCH] x86/CPU/AMD: Clear RDRAND CPUID bit on AMD family 15h/16h Lendacky, Thomas
2019-08-14 23:24 ` Non-random RDRAND " Pavel Machek
2019-08-14 23:38   ` Pavel Machek
2019-08-15 13:01   ` Lendacky, Thomas
2019-08-15 15:12   ` Theodore Y. Ts'o
2019-08-16  9:07     ` Pavel Machek
2019-08-16 14:42     ` Neil Horman
2019-08-15  7:21 ` Borislav Petkov
2019-08-15 13:47   ` Lendacky, Thomas
2019-08-15 15:34     ` Borislav Petkov [this message]
2019-08-15 20:14       ` Thomas Gleixner
2019-08-15 20:59 ` Andrew Cooper
2019-08-15 21:04   ` Thomas Gleixner
2019-08-15 21:05   ` Borislav Petkov
2019-08-15 21:25     ` Andrew Cooper
2019-08-17  8:44       ` Borislav Petkov
2019-08-17 11:43         ` Andrew Cooper
2019-08-18 16:32           ` Thomas Gleixner
2019-08-16 15:19 ` Andy Lutomirski

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