> > 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.)
