Re: [PATCH] KVM: arm64: Add missing hyp_enter when trapping sysreg

[Vincent Donnefort <vdonnefort@google.com>]

On Wed, Jun 17, 2026 at 11:28:11AM +0100, Fuad Tabba wrote:
> On Wed, 17 Jun 2026 at 10:55, Vincent Donnefort <vdonnefort@google.com> wrote:
> >
> > Add a missing hypervisor event call for hyp_enter on sysreg trapping,
> > causing an unbalanced hyp_enter/hyp_exit.
> >
> > The enum hyp_enter_exit_reason is not ABI, so we can keep the ERET
> > reasons at the end for clarity.
> >
> > Fixes: 696dfec22b8e ("KVM: arm64: Add hyp_enter/hyp_exit events to nVHE/pKVM hyp")
> > Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
> 
> One thing that caught my eye (as Sashiko would say: pre-existing, not
> introduced here), __hyp_enter_exit_reason_str() relies on positional
> correspondence between strs[] and enum hyp_enter_exit_reason, with no
> compile-time check. Inserting a new value in the middle of the enum
> (as you do here) silently shifts all the strings after it if the table
> isn't updated in lockstep.
> 
> A BUILD_BUG_ON(ARRAY_SIZE(strs)...) would at least catch size
> mismatches; catching ordering bugs is harder without per-entry
> initialisers like [HYP_REASON_SYS] = "sys".

Both are declared in a different file. You're correct this would be less error
prone to define [ XXX ] = "xxx". Perhaps I should convert that later.

> 
> Something for a future patch, for now:
> 
> Reviewed-by: Fuad Tabba <tabba@google.com>
> Tested-by: Fuad Tabba <tabba@google.com>

Thanks!

> 
> Cheers,
> /fuad
> 
> 
> >
> > diff --git a/arch/arm64/include/asm/kvm_hypevents.h b/arch/arm64/include/asm/kvm_hypevents.h
> > index 743c49bd878f..5f6e6789d121 100644
> > --- a/arch/arm64/include/asm/kvm_hypevents.h
> > +++ b/arch/arm64/include/asm/kvm_hypevents.h
> > @@ -12,6 +12,7 @@
> >  enum hyp_enter_exit_reason {
> >         HYP_REASON_SMC,
> >         HYP_REASON_HVC,
> > +       HYP_REASON_SYS,
> >         HYP_REASON_PSCI,
> >         HYP_REASON_HOST_ABORT,
> >         HYP_REASON_GUEST_EXIT,
> > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > index 06db299c37a8..45a4abb9619d 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > @@ -913,6 +913,7 @@ void handle_trap(struct kvm_cpu_context *host_ctxt)
> >                 handle_host_mem_abort(host_ctxt);
> >                 break;
> >         case ESR_ELx_EC_SYS64:
> > +               trace_hyp_enter(host_ctxt, HYP_REASON_SYS);
> >                 if (handle_host_mte(esr))
> >                         break;
> >                 fallthrough;
> > diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
> > index c4b3ee552131..c84434e2349a 100644
> > --- a/arch/arm64/kvm/hyp_trace.c
> > +++ b/arch/arm64/kvm/hyp_trace.c
> > @@ -398,6 +398,7 @@ static const char *__hyp_enter_exit_reason_str(u8 reason)
> >         static const char strs[][12] = {
> >                 "smc",
> >                 "hvc",
> > +               "sys",
> >                 "psci",
> >                 "host_abort",
> >                 "guest_exit",
> >
> > base-commit: 8cd9520d35a6c38db6567e97dd93b1f11f185dc6
> > --
> > 2.54.0.1136.gdb2ca164c4-goog
> >