Re: [PATCH 2/6] arm64: errata: Add QCOM_KRYO_2XX_GOLD to the spectre_bhb_firmware_mitigated_list

[Dmitry Baryshkov]

On Mon, Dec 09, 2024 at 03:34:59PM -0800, Julius Werner wrote:
> > > NOTE: presumably this patch won't actually do much on its own because
> > > (I believe) it requires a firmware update to go with it.
> >
> > Why? is_spectre_bhb_fw_affected() returns true if (cpu in list OR fw
> > mitigated)
> 
> That affects reporting, but the mitigation works by making an
> ARM_SMCCC_ARCH_WORKAROUND_3 Secure Monitor Call to firmware, and that
> only works if that call is implemented in firmware. Trusted-Firmware-A
> is currently the only open source firmware I'm aware of that
> implements this call, and it only supports Kryo 4 and 6 upstream (not
> 2 or 3).
> 
> So in order for this patch to actually be able to do anything other
> than report that the mitigation is missing, it would need to run on
> devices that either use a downstream fork of TF-A with added Kryo 2/3
> support (I doubt this exists because AFAIK Kryo 4 was Qualcomm's first
> attempt to use TF-A) or use some other proprietary kind of Secure
> Monitor firmware that has this SMC and mitigation implemented
> separately. (It seems unlikely that Qualcomm did this in their QTEE
> firmware, since if they had they would have probably also added the
> MIDRs here to Linux to activate it.)

Ack, thanks for the detailed explanation.

-- 
With best wishes
Dmitry