Re: [PATCH v4 11/18] KVM: arm64: Stub implementation of non-protected nVHE HYP stack unwinder

[Marc Zyngier]

On 2022-07-18 17:51, Kalesh Singh wrote:
> On Mon, Jul 18, 2022 at 12:31 AM Marc Zyngier <maz@xxxxxxxxxx> wrote:
> > On Fri, 15 Jul 2022 07:10:20 +0100,
> > Kalesh Singh <kaleshsingh@xxxxxxxxxx> wrote:
> > >
> > > Add stub implementations of non-protected nVHE stack unwinder, for
> > > building. These are implemented later in this series.
> > >
> > > Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
> > > ---
> > >  arch/arm64/include/asm/stacktrace/nvhe.h | 22 ++++++++++++++++++++++
> > >  1 file changed, 22 insertions(+)
> > >
> > > diff --git a/arch/arm64/include/asm/stacktrace/nvhe.h b/arch/arm64/include/asm/stacktrace/nvhe.h
> > > index 1eac4e57f2ae..36cf7858ddd8 100644
> > > --- a/arch/arm64/include/asm/stacktrace/nvhe.h
> > > +++ b/arch/arm64/include/asm/stacktrace/nvhe.h
> > > @@ -8,6 +8,12 @@
> > >   *      the HYP memory. The stack is unwinded in EL2 and dumped to a shared
> > >   *      buffer where the host can read and print the stacktrace.
> > >   *
> > > + *   2) Non-protected nVHE mode - the host can directly access the
> > > + *      HYP stack pages and unwind the HYP stack in EL1. This saves having
> > > + *      to allocate shared buffers for the host to read the unwinded
> > > + *      stacktrace.
> > > + *
> > > + *
> > >   * Copyright (C) 2022 Google LLC
> > >   */
> > >  #ifndef __ASM_STACKTRACE_NVHE_H
> > > @@ -53,5 +59,21 @@ static int notrace unwind_next(struct unwind_state *state)
> > >  NOKPROBE_SYMBOL(unwind_next);
> > >  #endif       /* CONFIG_PROTECTED_NVHE_STACKTRACE */
> > >
> > > +/*
> > > + * Non-protected nVHE HYP stack unwinder
> > > + */
> > > +#else        /* !__KVM_NVHE_HYPERVISOR__ */
> >
> > I don't get this path. This either represents the VHE hypervisor or
> > the kernel proper. Which one is it?
>
> Hi Marc. This is run from kernel proper context. And it's the
> unwinding for conventional nVHE (non-protected). The unwinding is done
> from the host kernel in EL1.

This really deserves a comment here, as the one you currently
have is a bit misleading (and you probably want to move it
below the #else).

Thanks,

        M.
--
Jazz is not dead. It just smells funny...