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

[Kalesh Singh]

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 at 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)
 	 */
 	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