[PATCH 5/7] KVM: arm64: Add Hyp overflow stack

[Kalesh Singh <kaleshsingh@google.com>]

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/setup.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/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 114053dff228..39937fa6a1b2 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -20,6 +20,11 @@
 
 unsigned long hyp_nr_cpus;
 
+#ifdef CONFIG_NVHE_EL2_DEBUG
+DEFINE_PER_CPU(unsigned long [PAGE_SIZE/sizeof(long)], hyp_overflow_stack)
+	__aligned(16);
+#endif
+
 #define hyp_percpu_size ((unsigned long)__per_cpu_end - \
 			 (unsigned long)__per_cpu_start)
 
-- 
2.35.1.265.g69c8d7142f-goog