[PATCH v4 00/18] KVM: arm64: Confine protected VM vCPU state to EL2

Thu Oct 1 07:31:55 PDT 2026

Hi Marc,

Here's a link to the series based on kvmarm/next, conflicts resolved:

https://android-kvm.googlesource.com/linux/+/refs/heads/tabba/pkvm-core-b-v4-kvmarm-next

Cheers,
/fuad

On Thu, 1 Oct 2026 at 14:57, Fuad Tabba <fuad.tabba at linux.dev> wrote:
>
> Hi folks,
>
> Changes since v3 [1]:
>   - A protected vCPU that EL2 holds powered off reads as
>     KVM_MP_STATE_UNINITIALIZED, in place of a new bool. (Marc)
>   - The marshalling and PSCI patches access the host copy through the
>     vCPU accessors, with every assignment on one line. (Marc)
>   - The PC adjustment pair is kvm_adjust_pc_get()/put() and tests for
>     the hyp vCPU directly. (Marc)
>   - CPU_OFF clears the reset flag before its release of OFF, CPU_ON's
>     relaxed cmpxchg is ordered by its control dependency, and the
>     CPU_ON rollback stores OFF with a release. pkvm_reset_vcpu()
>     carries the CPU_ON/CPU_OFF sequence as a comment and drops its
>     WARN_ON(). (Vincent, Will)
>   - Collected Reviewed-bys.
>
> Following the vCPU state-sync series [3], this series completes the
> job for protected VMs: a protected guest's register state stays at
> EL2, and the host sees only what handling each exit requires.
>
> EL2 marshals a protected vCPU's state per exception class instead of
> copying the whole context both ways. It owns the vCPU's trap
> configuration, system register reset and HVC handling, and implements
> PSCI itself: AFFINITY_INFO is left to the host, and CPU_ON and CPU_OFF
> are resolved at EL2 with the host only scheduling the target or
> stopping it. A protected guest's TRNG calls, which the host handled
> until now, return NOT_SUPPORTED until TRNG for protected guests
> follows. EL2 implements PSCI 1.1, so a protected guest also loses the
> functions the host supports above that version, SYSTEM_OFF2 included.
> Host ioctls that would reach the state EL2 owns fail with -EPERM, so a
> protected VM's state isn't save/restorable. All of this is scoped
> to KVM_VM_TYPE_ARM_PROTECTED, and pkvm.rst describes the resulting API.
>
> The kvmtool changes that go with this are posted separately [4].
>
> Patches 1 to 3 go out separately: the HCR_EL2.VSE fix [5], and the
> host vCPU VM read and pin fixes, patches 4 and 5 of the host hypercall
> fixes series [2]. None of the three is part of this series. They're
> carried so the series applies as is and Sashiko can run on it.
>
> The KVM_ARM_PREFERRED_TARGET documentation fix [6] went out just ahead
> of v1. Nothing here depends on it to apply, but patch 18 documents vCPU
> feature availability as something the capabilities report, while
> api.rst 4.83 still points userspace at a bitmap that has always been
> empty.
>
> The series is structured as follows:
>
>   01:     The HCR_EL2.VSE fix, posted separately.
>   02-03:  The host vCPU VM read and pin fixes, posted separately.
>   04:     Steal time disabled for protected VMs.
>   05-06:  Per-exception-class entry handlers; EL2 owns a protected
>           vCPU's trap configuration.
>   07-09:  Timer state, system register reset and HVC handling at EL2.
>   10-11:  PSCI at EL2, and the KVM_ARM_VCPU_INIT and PSCI version
>           restrictions.
>   12-14:  Host PC adjustments blocked; an UNDEF at EL2 for exit
>           classes the host doesn't emulate; per-class state
>           marshalling.
>   15-16:  Host changes to private state, and host power-on of a vCPU
>           EL2 holds powered off, rejected.
>   17:     Capability allowlist.
>   18:     Documentation.
>
> Still to come: selftests, TRNG, self-hosted debug and SVE for protected
> guests, and much more, as separate series.
>
> Based on v7.3-rc3 (fd73f4a665989).
>
> Cheers,
> /fuad
>
> [1] https://lore.kernel.org/all/20260914113338.159227-1-fuad.tabba@linux.dev/
> [2] https://lore.kernel.org/all/20260915123846.2317931-1-fuad.tabba@linux.dev/
> [3] https://lore.kernel.org/all/20260729131823.2021516-1-fuad.tabba@linux.dev/
> [4] https://lore.kernel.org/all/20260831192406.1341841-1-fuad.tabba@linux.dev/
> [5] https://lore.kernel.org/all/20260829071120.2522788-1-fuad.tabba@linux.dev/
> [6] https://lore.kernel.org/all/20260831162815.269851-1-fuad.tabba@linux.dev/
>
> Fuad Tabba (16):
>   KVM: arm64: Sync HCR_EL2.VSE back to the host vCPU under pKVM
>   KVM: arm64: Validate the host vCPU's VM before reading it under pKVM
>   KVM: arm64: Pin the host vCPU before adjusting its PC under pKVM
>   KVM: arm64: Disable steal time for protected VMs
>   KVM: arm64: Skip fixed-feature state flush for protected vCPUs
>   KVM: arm64: Add system register reset framework for protected VMs
>   KVM: arm64: Implement HVC handling for protected guests at EL2
>   KVM: arm64: Handle PSCI calls for protected VMs at EL2
>   KVM: arm64: Restrict KVM_ARM_VCPU_INIT and PSCI version for protected
>     VMs
>   KVM: arm64: Prevent host PC adjustments for protected vCPUs
>   KVM: arm64: Inject an UNDEF at EL2 for unhandled protected guest exits
>   KVM: arm64: Add per-EC entry/exit state marshalling for protected
>     guests
>   KVM: arm64: Reject host access to protected VM private state
>   KVM: arm64: Reject host power-on of a vCPU that EL2 holds powered off
>   KVM: arm64: Advertise the capabilities that protected VMs support
>   KVM: arm64: Document the protected VM userspace API
>
> Marc Zyngier (2):
>   KVM: arm64: Introduce per-EC entry handlers for pKVM
>   KVM: arm64: Add {flush,sync}_hyp_timer_state() primitives
>
>  Documentation/virt/kvm/api.rst                |  27 +-
>  .../virt/kvm/arm/fw-pseudo-registers.rst      |   2 +
>  Documentation/virt/kvm/arm/pkvm.rst           | 164 ++++-
>  Documentation/virt/kvm/devices/vcpu.rst       |   3 +-
>  arch/arm64/include/asm/kvm_host.h             |  22 +-
>  arch/arm64/include/asm/kvm_hyp.h              |   4 +
>  arch/arm64/include/asm/kvm_pkvm.h             |  33 +
>  arch/arm64/kvm/arm.c                          |  76 ++-
>  arch/arm64/kvm/guest.c                        |  11 +
>  arch/arm64/kvm/hyp/exception.c                |  26 +-
>  arch/arm64/kvm/hyp/include/hyp/adjust_pc.h    |  48 ++
>  arch/arm64/kvm/hyp/include/nvhe/pkvm.h        |  20 +
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c            | 595 +++++++++++++++++-
>  arch/arm64/kvm/hyp/nvhe/pkvm.c                | 422 ++++++++++++-
>  arch/arm64/kvm/hyp/nvhe/switch.c              |  29 +-
>  arch/arm64/kvm/hyp/nvhe/sys_regs.c            |  60 ++
>  arch/arm64/kvm/hypercalls.c                   |   7 +
>  arch/arm64/kvm/pkvm.c                         |  21 +-
>  arch/arm64/kvm/psci.c                         |  11 +-
>  arch/arm64/kvm/pvtime.c                       |  10 +-
>  20 files changed, 1503 insertions(+), 88 deletions(-)
>
>
> base-commit: fd73f4a6659897191fa0d40695fe370925dd3780
> --
> 2.39.5
>