The ARM Cortex-A53 CPU cores and QGIC2 interrupt controller
(an implementation of the ARM GIC 2.0 specification) used in MSM8916
support virtualization, e.g. for KVM on Linux. However, so far it was
not possible to make use of this functionality, because Qualcomm's
proprietary "hyp" firmware blocks the EL2 mode of the CPU and only
allows booting Linux in EL1.

However, on devices without (firmware) secure boot there is no need
to rely on all of Qualcomm's firmware. The "hyp" firmware on MSM8916
seems simple enough that it can be replaced with an open-source
alternative created only based on trial and error - with some similar
EL2/EL1 initialization code adapted from Linux and U-Boot.

qhypstub [1] is such an open-source firmware for MSM8916 that
can be used as drop-in replacement for Qualcomm's "hyp" firmware.
It does not implement any hypervisor functionality.
Instead, it allows booting Linux/KVM (or other hypervisors) in EL2.

With Linux booting in EL2, KVM seems to be working just fine on MSM8916.
However, so far it is not possible to make use of the virtualization
features in the GICv2. To use KVM's VGICv2 code, the QGIC2 device tree
node needs additional resources (according to binding documentation):

  - The CPU interface region (second reg) must be at least 8 KiB large
    to access the GICC_DIR register (mapped at 0x1000 offset)
  - Virtual control/CPU interface register base and size
  - Hypervisor maintenance interrupt

Fortunately, the public APQ8016E TRM [2] provides the required information:

  - The CPU interface region (at 0x0B002000) actually has a size of 8 KiB
  - Virtual control/CPU interface register is at 0x0B001000/0x0B004000
  - Hypervisor maintenance interrupt is "PPI #0"
      Note: This is a bit strange since almost all other ARM SoCs use
            GIC_PPI 9 for this. However, I have verified that this is
            indeed the interrupt that fires when bits are set in GICH_HCR.

Add the additional resources to the QGIC2 device tree node in msm8916.dtsi.
There is no functional difference when Linux is started in EL1 since the
additional resources are ignored in that case.

With these changes (and qhypstub), KVM seems to be fully working on
the DragonBoard 410c (apq8016-sbc) and BQ Aquaris X5 (longcheer-l8910).

[1]: https://github.com/msm8916-mainline/qhypstub
[2]: https://developer.qualcomm.com/download/sd410/snapdragon-410e-technical-reference-manual.pdfAcked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20210407163648.4708-1-stephan@gerhold.netSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>