[PATCH v2 7/9] KVM: arm64: Add hypervisor overflow stack

Kalesh Singh
2022-02-22T17:00:42Z

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 78e4b612ac06..751a4b9e429f 100644
--- a/arch/arm64/kvm/hyp/nvhe/host.S
+++ b/arch/arm64/kvm/hyp/nvhe/host.S
@@ -171,6 +171,10 @@ 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
@@ -178,6 +182,7 @@ 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 5a2e1ab79913..2accc158210f 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