Re: [PATCH v3] tpm: Disable RNG for all AMD fTPMs

["Jason A. Donenfeld" <Jason@zx2c4.com>]

On Thu, Aug 03, 2023 at 01:24:28PM -0500, Mario Limonciello wrote:
> The TPM RNG functionality is not necessary for entropy when the CPU
> already supports the RDRAND instruction. The TPM RNG functionality
> was previously disabled on a subset of AMD fTPM series, but reports
> continue to show problems on some systems causing stutter root caused
> to TPM RNG functionality.
> 
> Expand disabling TPM RNG use for all AMD fTPMs whether they have versions
> that claim to have fixed or not. To accomplish this, move the detection
> into part of the TPM CRB registration and add a flag indicating that
> the TPM should opt-out of registration to hwrng.
> 
> Cc: stable@vger.kernel.org # 5.5+
> Fixes: b006c439d58d ("hwrng: core - start hwrng kthread also for untrusted sources")
> Fixes: f1324bbc4011 ("tpm: disable hwrng for fTPM on some AMD designs")
> Fixes: 3ef193822b25 ("tpm_crb: fix fTPM on AMD Zen+ CPUs")
> Reported-by: daniil.stas@posteo.net
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217719
> Reported-by: bitlord0xff@gmail.com
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217212
> Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>

LGTM. Jarkko - can you replace the commit in your staging tree with this
one?