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From:   Kalesh Singh <kaleshsingh@google.com>
Date:   Mon, 18 Jul 2022 10:32:52 -0700
Message-ID: <CAC_TJvcc0VZhp+u+2YpXuQ-UcGC+YTKy1PEoPCmbm+_WXo6cVw@mail.gmail.com>
Subject: Re: [PATCH v4 12/18] KVM: arm64: Save protected-nVHE (pKVM) hyp stacktrace
To:     Marc Zyngier <maz@kernel.org>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Mark Brown <broonie@kernel.org>,
        "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>,
        Will Deacon <will@kernel.org>,
        Quentin Perret <qperret@google.com>,
        Fuad Tabba <tabba@google.com>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        andreyknvl@gmail.com, russell.king@oracle.com,
        vincenzo.frascino@arm.com, Masami Hiramatsu <mhiramat@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrew Jones <drjones@redhat.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Marco Elver <elver@google.com>, Keir Fraser <keirf@google.com>,
        Zenghui Yu <yuzenghui@huawei.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Oliver Upton <oupton@google.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@lists.infradead.org>,
        kvmarm <kvmarm@lists.cs.columbia.edu>,
        LKML <linux-kernel@vger.kernel.org>, android-mm@google.com,
        "Cc: Android Kernel" <kernel-team@android.com>
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On Mon, Jul 18, 2022 at 2:36 AM Marc Zyngier <maz@kernel.org> wrote:
>
> On Fri, 15 Jul 2022 07:10:21 +0100,
> Kalesh Singh <kaleshsingh@google.com> wrote:
> >
> > In protected nVHE mode, the host cannot access private owned hypervisor
> > memory. Also the hypervisor aims to remains simple to reduce the attack
> > surface and does not provide any printk support.
> >
> > For the above reasons, the approach taken to provide hypervisor stacktraces
> > in protected mode is:
> >    1) Unwind and save the hyp stack addresses in EL2 to a shared buffer
> >       with the host (done in this patch).
> >    2) Delegate the dumping and symbolization of the addresses to the
> >       host in EL1 (later patch in the series).
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> > ---
> >  arch/arm64/include/asm/stacktrace/nvhe.h | 18 ++++++
> >  arch/arm64/kvm/hyp/nvhe/stacktrace.c     | 70 ++++++++++++++++++++++++
> >  2 files changed, 88 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/stacktrace/nvhe.h b/arch/arm64/include/asm/stacktrace/nvhe.h
> > index 36cf7858ddd8..456a6ae08433 100644
> > --- a/arch/arm64/include/asm/stacktrace/nvhe.h
> > +++ b/arch/arm64/include/asm/stacktrace/nvhe.h
> > @@ -21,6 +21,22 @@
> >
> >  #include <asm/stacktrace/common.h>
> >
> > +/**
> > + * kvm_nvhe_unwind_init - Start an unwind from the given nVHE HYP fp and pc
> > + *
> > + * @fp : frame pointer at which to start the unwinding.
> > + * @pc : program counter at which to start the unwinding.
> > + */
> > +static __always_inline void kvm_nvhe_unwind_init(struct unwind_state *state,
> > +                                              unsigned long fp,
> > +                                              unsigned long pc)
> > +{
> > +     unwind_init_common(state, NULL);
>
> Huh. Be careful here. This function is only 'inline', which means it
> may not be really inlined. We've had tons of similar issues like this
> in the past, and although this will not break at runtime anymore, it
> will definitely stop the kernel from linking.

Ahh, there are a few other always inline *unwind_init* functions that
use this. I'll update in the next version.

Thanks,
Kalesh

>
> Thanks,
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.