** Description changed:
SRU Justification:
[Impact]
- Google has requested a backport of some upstream arm64 and KVM architecture
- HCR_EL2.E2H related patches to the Noble kernel linux-gcprelease.
+ Google has requested a backport of upstream arm64 and KVM architecture
+ HCR_EL2.E2H related patches to the Noble kernel linux-gcp. These patches
+ introduce architectural support for FEAT_E2H0, which governs platforms
+ omitting support for running a host at exception level 1 (EL1) without
+ Virtualization Host Extensions (VHE). Under the ARMv9.5 specification
+ (and retroactively permitted since ARMv8.1), implementations can choose to
+ have VHE as the only execution behavior, meaning that HCR_EL2.E2H acts as
+ RES1 (Read As Standard 1) and HCR_EL2.NV1 can be implemented as RES0.
+ Because individual patches in the series introduced tightly coupled edge-case
+ bugs that were sequentially resolved by the later commits, the entire
sequence
+ must be backported as an atomic block to Noble release.
[Fix]
Target patches:
3944382fa6f2 ("arm64: Treat HCR_EL2.E2H as RES1 when ID_AA64MMFR4_EL1.E2H0 is
negative")
b3320142f3db ("arm64: Fix early handling of FEAT_E2H0 not being implemented")
7a68b55ff39b ("KVM: arm64: Initialize HCR_EL2.E2H early")
ca88ecdce5f5 ("arm64: Revamp HCR_EL2.E2H RES1 detection")
Some additional patches may be needed for these to apply/build cleanly
[Test Plan]
Copile tested
Boot test
[Regression potential]
The regression potential is isolated strictly to ARM64 (aarch64)
platforms, with zero risk to x86 or other architectures. Because these
patches alter register initialization logic (HCR_EL2) at very early boot
and hypervisor init stages, regressions could manifest as boot failures,
kernel panics during early CPU feature detection, or broken nested
virtualization on specific ARM hardware implementations. However, this
risk is deeply mitigated by pulling the entire 4-commit sequence as a
comprehensive lifecycle block, directly mirroring stable upstream
patterns (such as those fed by the 6.12 stable branches).
[Other Info]
SF:00442966
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https://bugs.launchpad.net/bugs/2160745
Title:
KVM backports to 6.8 related to HCR_EL2.E2H
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