Anders Andersson wrote: > On Sun, Aug 13, 2023 at 11:09 PM Björn Persson <Bjorn@rombobjörn.se> wrote: > > Jeffrey Walton wrote: > > > Maybe related to > > > https://www.phoronix.com/news/Linux-Disables-RNG-AMD-fTPMs > > > > Not likely. That article is about a firmware TPM that comes with newer > > Ryzen processors. Older Ryzens supposedly don't have it. The processor > > in my APU2 is a GX-412TC, not a Ryzen at all, and my TPM is a discrete > > chip from Infineon. The change in question is supposed to disable the > > random number generator only if the TPM lists AMD as its manufacturer. > > I agree that the patch looks ok, but I remember being hit by a kernel > change that inadvertently changed the behavior on other systems too > (ECC RAM background scrubbing), but nobody really noticed because it > was not in much use. > > I suspect that the case of having an external TPM on an AMD system is > such an unusual case, and I couldn't trace exactly where that patch > checked the AMD string, so perhaps it's picking up the AMD string > earlier on, and decides to disable all TPM on the AMD system. At least > the timing of the problem and the patch is suspicious.
I see the 6.1 branch contains the first attempt at working around the stutter problem, which disables randomness only from certain known broken firmware versions: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/char/tpm/tpm-chip.c?h=linux-6.1.y#n510 It's supposed to log a warning when it takes effect: "AMD fTPM version 0x%llx causes system stutter; hwrng disabled\n" That message does not appear in my logs. The new workaround, which disables randomness from all AMD firmware TPUs and doesn't log, can be in effect only if it has been backported to Debian's kernel very recently. That does not seem to be the case, if this is the right way to look for backports: https://salsa.debian.org/kernel-team/linux/-/commits/bookworm/ I'll check what the manufacturer number is on my system, if I can figure out how to get at it. Björn Persson
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