linux-kernel - Re: [PATCH 2/6] arm64: errata: Add QCOM_KRYO_2XX_GOLD to the spectre_bhb_firmware_mitigated

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Message-ID: <CAODwPW8mq-saJuTYnMhA6bCopcjQwBxEoyWhQB60Jg1m7wUZkw@mail.gmail.com>
Date: Mon, 9 Dec 2024 15:34:59 -0800
From: Julius Werner <jwerner@...omium.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Douglas Anderson <dianders@...omium.org>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Julius Werner <jwerner@...omium.org>, Jeffrey Hugo <quic_jhugo@...cinc.com>, 
	Roxana Bradescu <roxabee@...gle.com>, bjorn.andersson@....qualcomm.com, 
	linux-arm-kernel@...ts.infradead.org, Trilok Soni <quic_tsoni@...cinc.com>, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] arm64: errata: Add QCOM_KRYO_2XX_GOLD to the spectre_bhb_firmware_mitigated_list

> > 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.)