Re: [PATCH v1 2/3] KVM: arm64: Add guest_hvc hyp event

[Vincent Donnefort <vdonnefort@google.com>]

On Fri, Oct 09, 2026 at 01:06:05PM +0100, Fuad Tabba wrote:
> Hi Vincent,
> 
> On Fri, 09 Oct 2026 09:45:28 +0100, Vincent Donnefort
> <vdonnefort@google.com> wrote:
> 
> > Add a guest_hvc hypervisor trace event to log protected VM HVC call IDs,
> > return values, and whether the call was handled by the hypervisor.
> 
> nit: only the first return value is logged.
> 
> [...]
> > diff --git a/arch/arm64/include/asm/kvm_hypevents.h b/arch/arm64/include/asm/kvm_hypevents.h
> 
> [...]
> > +HYP_EVENT(guest_hvc,
> > +        HE_PROTO(u32 id, u64 val, u8 handled),
> > +        HE_STRUCT(
> > +                he_field(u8, handled)
> > +                he_field(u32, id)
> > +                he_field(u64, val)
> > +        ),
> 
> remote_event_format_show() doesn't align the field offsets, so the
> format file puts id at 3 and val at 7 instead of 4 and 8. hyp_enter's
> vcpu is already off the same way, so should this be a separate fix in
> trace_remote.c, with ALIGN(offset, field->align)?

Ha, absolutely, I'll send something to linux-trace. We don't have this issue in
Android kernel because the struct are __packed there.

> 
> [...]
> > diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
> 
> [...]
> > @@ -1183,5 +1185,8 @@ bool kvm_handle_pvm_hvc64(struct kvm_vcpu *vcpu, u64 *exit_code)
> >
> >          if (handled)
> >                  smccc_set_retval(vcpu, val[0], val[1], val[2], val[3]);
> > +
> > +        trace_guest_hvc(fn, val[0], handled);
> > +
> >          return handled;
> 
> When handled is false, val[0] is the SMCCC_RET_INVALID_PARAMETER
> initialiser, which the guest never gets. For example, a MEM_SHARE
> forwarded to the host logs "id=0xc6000003 val=0xfffffffffffffffd
> handled=0". Could this log 0 in that case?

Ack. That shouldn't be too difficult

> 
> Cheers,
> /fuad

-- 
Vincent