linux-kernel - Re: [PATCH 4.19 72/98] x86/CPU/AMD: Clear RDRAND CPUID bit on AMD family 15h/16h

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Date:   Thu, 29 Aug 2019 00:05:33 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Pavel Machek <pavel@...x.de>, Borislav Petkov <bp@...en8.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chen Yu <yu.c.chen@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 4.19 72/98] x86/CPU/AMD: Clear RDRAND CPUID bit on AMD
 family 15h/16h

On Wed 2019-08-28 16:15:06, Thomas Gleixner wrote:
> On Wed, 28 Aug 2019, Pavel Machek wrote:
> > On Wed 2019-08-28 14:46:21, Borislav Petkov wrote:
> > > On Wed, Aug 28, 2019 at 02:29:13PM +0200, Pavel Machek wrote:
> > > > This is not a way to have an inteligent conversation.
> > > 
> > > No, this *is* the way to keep the conversation sane, without veering
> > > off into some absurd claims.
> > > 
> > > So, to cut to the chase: you can simply add "rdrand=force" to your
> > > cmdline parameters and get back to using RDRAND.
> > > 
> > > And yet if you still feel this fix does not meet your expectations,
> > > you were told already to either produce patches or who to contact. I'm
> > > afraid complaining on this thread won't get you anywhere but that's your
> > > call.
> > 
> > No, this does not meet my expectations, it violates stable kernel
> > rules, and will cause regression to some users, while better solution
> > is known to be available.
> 
> Your unqualified ranting does not meet my expectation either and it
> violates any rule of common sense.
> 
> For the record:
> 
>   Neither AMD nor we have any idea which particular machines have a fixed
>   BIOS and which have not. There is no technical indicator either at boot
>   time as the wreckage manifests itself only after resume.
> 
>   So in the interest of users the only sensible decision is to disable
>   RDRAND for this class of CPUs.

No.

Obviously best solution would be microcode update to fix the problem,
or to enable kernel to fix the problem.

>   If you have a list of machines which have a fixed BIOS, then provide it
>   in form of patches. If not then stop claiming that there is a better
>   solution available.

And yes, whitelist would be already better than present solution. It is
not my duty to submit fixes to your proposed patch.

> Anyway, I'm done with that and further rants of yours go directly to
> /dev/null.
> 
> Thanks for wasting everyones time

Thanks for your profesional attitude.

								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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