linux-kernel - Re: [regression] Bug 216989 - since 6.1 systems with AMD Ryzen stutter when fTPM is enabled

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Date:   Wed, 8 Feb 2023 04:13:37 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Linux regressions mailing list <regressions@...ts.linux.dev>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>,
        linux-integrity@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, reach622@...lcuk.com,
        1138267643@...com, "Jason A. Donenfeld" <Jason@...c4.com>
Subject: Re: [regression] Bug 216989 - since 6.1 systems with AMD Ryzen
 stutter when fTPM is enabled

On Wed, Feb 08, 2023 at 04:13:16AM +0200, Jarkko Sakkinen wrote:
> On Thu, Feb 02, 2023 at 07:57:37AM -0500, James Bottomley wrote:
> > On Thu, 2023-02-02 at 11:28 +0100, Linux kernel regression tracking
> > (Thorsten Leemhuis) wrote:
> > [...]
> > > So it's a firmware problem, but apparently one that Linux only
> > > triggers since 6.1.
> > > 
> > > Jason, could the hwrng changes have anything to do with this?
> > > 
> > > A bisection really would be helpful, but I guess that is not easy as
> > > the problem apparently only shows up after some time...
> > 
> > the problem description says the fTPM causes system stutter when it
> > writes to NVRAM.  Since an fTPM is a proprietary implementation, we
> > don't know what it does.  The ms TPM implementation definitely doesn't
> > trigger NV writes on rng requests, but it is plausible this fTPM does
> > ... particularly if they have a time based input to the DRNG.  Even if
> > this speculation is true, there's not much we can do about it, since
> > it's a firmware bug and AMD should have delivered the BIOS update that
> > fixes it.
> > 
> > The way to test this would be to set the config option
> > 
> > CONFIG_HW_RANDOM_TPM=n
> > 
> > and see if the stutter goes away.  I suppose if someone could quantify
> > the bad bioses, we could warn, but that's about it.
> > 
> > James
> > 
> 
> And e.g. I do not have a Ryzen CPU so pretty hard to answer such question.

... about hwrng

BR, Jarkko