linux-kernel - Re: [PATCH v3 6/8] KVM: arm64: Add hypervisor overflow stack

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Date:   Thu, 24 Feb 2022 09:56:30 -0800
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     Fuad Tabba <tabba@...gle.com>
Cc:     Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>,
        Andrew Walbran <qwandor@...gle.com>,
        Andrew Scull <ascull@...gle.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        kvmarm@...ts.cs.columbia.edu, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 6/8] KVM: arm64: Add hypervisor overflow stack

On Thu, Feb 24, 2022 at 4:27 AM Fuad Tabba <tabba@...gle.com> wrote:
>
> Hi Kalesh,
>
> On Thu, Feb 24, 2022 at 5:21 AM Kalesh Singh <kaleshsingh@...gle.com> wrote:
> >
> > Allocate and switch to 16-byte aligned secondary stack on overflow. This
> > provides us stack space to better handle overflows; and is used in
> > a subsequent patch to dump the hypervisor stacktrace. The overflow stack
> > is only allocated if CONFIG_NVHE_EL2_DEBUG is enabled, as hypervisor
> > stacktraces is a debug feature dependent on CONFIG_NVHE_EL2_DEBUG.
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/host.S   | 5 +++++
> >  arch/arm64/kvm/hyp/nvhe/switch.c | 5 +++++
> >  2 files changed, 10 insertions(+)
> >
> > diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
> > index 749961bfa5ba..367a01e8abed 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/host.S
> > +++ b/arch/arm64/kvm/hyp/nvhe/host.S
> > @@ -179,6 +179,10 @@ SYM_FUNC_END(__host_hvc)
> >         b       hyp_panic
> >
> >  .L__hyp_sp_overflow\@:
> > +#ifdef CONFIG_NVHE_EL2_DEBUG
> > +       /* Switch to the overflow stack */
> > +       adr_this_cpu sp, hyp_overflow_stack + PAGE_SIZE, x0
> > +#else
> >         /*
> >          * Reset SP to the top of the stack, to allow handling the hyp_panic.
> >          * This corrupts the stack but is ok, since we won't be attempting
> > @@ -186,6 +190,7 @@ SYM_FUNC_END(__host_hvc)
> >          */
>
> Nit: Maybe you should update this comment as well, since whether it
> corrupts the stack or not depends on what happens above with
> CONFIG_NVHE_EL2_DEBUG.

Ack, will update it in the next version.

Thanks,
Kalesh
>
> Thanks,
> /fuad
>
> >         ldr_this_cpu    x0, kvm_init_params + NVHE_INIT_STACK_HYP_VA, x1
> >         mov     sp, x0
> > +#endif
> >
> >         bl      hyp_panic_bad_stack
> >         ASM_BUG()
> > diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> > index 703a5d3f611b..efc20273a352 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> > @@ -34,6 +34,11 @@ DEFINE_PER_CPU(struct kvm_host_data, kvm_host_data);
> >  DEFINE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt);
> >  DEFINE_PER_CPU(unsigned long, kvm_hyp_vector);
> >
> > +#ifdef CONFIG_NVHE_EL2_DEBUG
> > +DEFINE_PER_CPU(unsigned long [PAGE_SIZE/sizeof(long)], hyp_overflow_stack)
> > +       __aligned(16);
> > +#endif
> > +
> >  static void __activate_traps(struct kvm_vcpu *vcpu)
> >  {
> >         u64 val;
> > --
> > 2.35.1.473.g83b2b277ed-goog
> >