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

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Message-ID: <CAC_TJvewAfGACxwZ57W+fDsXOYBNnjxaKUt3Es9Ou0vDO3H_0w@mail.gmail.com>
Date:   Mon, 18 Jul 2022 09:51:39 -0700
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>,
        Will Deacon <will@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        Fuad Tabba <tabba@...gle.com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        andreyknvl@...il.com, russell.king@...cle.com,
        vincenzo.frascino@....com, Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Marco Elver <elver@...gle.com>, Keir Fraser <keirf@...gle.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Oliver Upton <oupton@...gle.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        LKML <linux-kernel@...r.kernel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>
Subject: Re: [PATCH v4 11/18] KVM: arm64: Stub implementation of non-protected
 nVHE HYP stack unwinder

On Mon, Jul 18, 2022 at 12:31 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Fri, 15 Jul 2022 07:10:20 +0100,
> Kalesh Singh <kaleshsingh@...gle.com> 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@...gle.com>
> > ---
> >  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.

>
> > +static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
> > +                                  struct stack_info *info)
> > +{
> > +     return false;
> > +}
> > +
> > +static int notrace unwind_next(struct unwind_state *state)
> > +{
> > +     return 0;
> > +}
> > +NOKPROBE_SYMBOL(unwind_next);
> > +
> >  #endif       /* __KVM_NVHE_HYPERVISOR__ */
> >  #endif       /* __ASM_STACKTRACE_NVHE_H */
>
> Thanks,
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.
>
> --
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>