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

From: Kalesh Singh <kaleshsingh@google.com>
To: Fuad Tabba <tabba@google.com>
Cc: Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Quentin Perret <qperret@google.com>,
	Suren Baghdasaryan <surenb@google.com>,
	"Cc: Android Kernel" <kernel-team@android.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>,
	Mark Rutland <mark.rutland@arm.com>,
	Mark Brown <broonie@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Peter Collingbourne <pcc@google.com>,
	"Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>,
	Andrew Walbran <qwandor@google.com>,
	Andrew Scull <ascull@google.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
	<linux-arm-kernel@lists.infradead.org>,
	kvmarm@lists.cs.columbia.edu, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 6/8] KVM: arm64: Add hypervisor overflow stack
Date: Thu, 24 Feb 2022 09:56:30 -0800	[thread overview]
Message-ID: <CAC_TJve3wW91UMtCNHeDSZ8hspySmuYO2WgEYEH3Dk=Uj+GkJw@mail.gmail.com> (raw)
In-Reply-To: <CA+EHjTwhpjDDnKRU3QrJysgMhYH7eTi2_LrWpxCArLoP-1-BrQ@mail.gmail.com>

On Thu, Feb 24, 2022 at 4:27 AM Fuad Tabba <tabba@google.com> wrote:
>
> Hi Kalesh,
>
> On Thu, Feb 24, 2022 at 5:21 AM Kalesh Singh <kaleshsingh@google.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@google.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
> >