[PATCH v1 0/4] trace_hyp_printk() for pKVM/nVHE hypervisor

[Fuad Tabba]

On Mon, 15 Jun 2026 at 09:28, Vincent Donnefort <vdonnefort at google.com> wrote:
>
> On Sun, Jun 14, 2026 at 01:57:56PM +0100, Fuad Tabba wrote:
> > Hi Vincent,
> >
> > On Fri, 12 Jun 2026 at 15:22, Vincent Donnefort <vdonnefort at google.com> wrote:
> > >
> > > Hi all,
> > >
> > > This series adds a hypervisor event "hyp_printk" which enables
> > > developers to log pretty much anything into the hypervisor tracing
> > > buffer, just like the kernel function trace_printk().
> > >
> > > This enables rich logging from the hypervisor, while leaving all the
> > > string parsing burden to the kernel. This has been the main way of
> > > debugging pKVM in Android.
> >
> > I tested the series on v7.1-rc7 under QEMU (cortex-a53 CPU, pKVM nVHE):
> > - Booted a host under pKVM with a non-protected kvmtool guest (npVM)
> > and a protected kvmtool guest (pVM).
> > - Functional test: added a temporary trace_hyp_printk() call site in
> > handle___kvm_vcpu_run() with 0-arg, 1-arg, and 2-arg calls. Mounted
> > tracefs, enabled the hyp_printk event, ran a kvmtool guest to trigger
> > vcpu_run, read the trace buffer. All expected entries appeared with
> > correctly formatted output.
>
> Thanks for the testing!
>
> >
> > One question: kvm_hyp_trace_init() returns early when
> > is_kernel_in_hyp_mode() is true. On VHE-capable hardware, pKVM uses
> > hVHE. So it seams that the entire hyp tracing subsystem (not just
> > hyp_printk) is non-functional in hVHE mode. Is hVHE support
> > intentionally deferred?
>
> You got me scared for a moment but I did try hVHE and it seems alright:
>
>   [    5.369985] kvm [1]: Protected hVHE mode initialized successfully
>
>   $ ls /sys/kernel/tracing/remotes/hypervisor/
>
> is_kernel_in_hyp_mode() just checks if the kernel is running at EL2 which it
> shouldn't in the hVHE case?

I'll try again and report back, must be user error.

/fuad

>
> >
> > Cheers,
> > /fuad
> >
> > >
> > > Even though not strictly related to trace_hyp_printk, I have added the
> > > following two patches:
> > >
> > >   * KVM: arm64: Allow early calls to pKVM host_share/unshare_hyp
> > >
> > >     This one mainly intends to support one of the new features I have
> > >     posted here [1], which allows to enable tracing as early as
> > >     possible. I have added it here to limit cross-posting.
> > >
> > >   * KVM: arm64: Move kvm_define_hypevents.h to arch/arm64/kvm/
> > >
> > >     This one is just a cleanup.
> > >
> > > [1] https://lore.kernel.org/all/20260605163825.1762953-1-vdonnefort@google.com/
> > >
> > > Vincent Donnefort (4):
> > >   KVM: arm64: Allow early calls to pKVM host_share/unshare_hyp
> > >   KVM: arm64: Move kvm_define_hypevents.h to arch/arm64/kvm/
> > >   tracing/remotes: Add REMOTE_EVENT_CUSTOM_PRINTK() helper
> > >   KVM: arm64: Add hyp_printk event to nVHE/pKVM hyp
> > >
> > >  arch/arm64/include/asm/kvm_asm.h              |  4 +-
> > >  arch/arm64/include/asm/kvm_hypevents.h        | 14 ++++
> > >  arch/arm64/include/asm/kvm_hyptrace.h         |  8 +++
> > >  arch/arm64/kernel/image-vars.h                |  1 +
> > >  arch/arm64/kernel/vmlinux.lds.S               |  4 ++
> > >  .../define_hypevents.h}                       |  0
> > >  .../kvm/hyp/include/nvhe/define_events.h      |  2 -
> > >  arch/arm64/kvm/hyp/include/nvhe/trace.h       | 65 +++++++++++++++++++
> > >  arch/arm64/kvm/hyp/nvhe/events.c              |  6 ++
> > >  arch/arm64/kvm/hyp/nvhe/hyp-main.c            |  2 +-
> > >  arch/arm64/kvm/hyp_trace.c                    | 60 ++++++++++++++++-
> > >  include/trace/define_remote_events.h          | 19 +++++-
> > >  12 files changed, 176 insertions(+), 9 deletions(-)
> > >  rename arch/arm64/{include/asm/kvm_define_hypevents.h => kvm/define_hypevents.h} (100%)
> > >
> > >
> > > base-commit: 4549871118cf616eecdd2d939f78e3b9e1dddc48
> > > --
> > > 2.54.0.1136.gdb2ca164c4-goog
> > >