2022-02-24 05:33:31

by Kalesh Singh

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

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 <[email protected]>
---
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)
*/
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

2022-02-24 16:32:33

by Fuad Tabba

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

Hi Kalesh,

On Thu, Feb 24, 2022 at 5:21 AM Kalesh Singh <[email protected]> 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 <[email protected]>
> ---
> 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.

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
>

2022-02-24 18:24:27

by Kalesh Singh

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

On Thu, Feb 24, 2022 at 4:27 AM Fuad Tabba <[email protected]> wrote:
>
> Hi Kalesh,
>
> On Thu, Feb 24, 2022 at 5:21 AM Kalesh Singh <[email protected]> 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 <[email protected]>
> > ---
> > 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
> >