Comment 0 for bug 1787993

[Impact]
Track: Spectre v4 mitigation (Speculative Store Bypass Disable) support for arm64 using SMC firmware call to set a hardware chicken bit. Patch now in 4.18 to Bionic.

[Test]

[Fix]
http://lkml.iu.edu/hypermail/linux/kernel/1805.2/05868.html

-- From 4.18 --
eff0e9e1078e arm/arm64: smccc: Add SMCCC-specific return codes
8e2906245f1e arm64: Call ARCH_WORKAROUND_2 on transitions between EL0 and EL1
5cf9ce6e5ea5 arm64: Add per-cpu infrastructure to call ARCH_WORKAROUND_2
a725e3dda181 arm64: Add ARCH_WORKAROUND_2 probing
a43ae4dfe56a arm64: Add 'ssbd' command-line option
c32e1736ca03 arm64: ssbd: Add global mitigation state accessor
986372c4367f arm64: ssbd: Skip apply_ssbd if not using dynamic mitigation
647d0519b53f arm64: ssbd: Restore mitigation status on CPU resume
9dd9614f5476 arm64: ssbd: Introduce thread flag to control userspace mitigation
85478bab4091 arm64: KVM: Add HYP per-cpu accessors
55e3748e8902 arm64: KVM: Add ARCH_WORKAROUND_2 support for guests the first line
b4f18c063a13 arm64: KVM: Handle guest's ARCH_WORKAROUND_2 requests
5d81f7dc9bca arm64: KVM: Add ARCH_WORKAROUND_2 discovery through ARCH_FEATURES_FUNC_ID

[Regression Potential]