[PATCH 2/4] 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.

Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
---
 arch/arm64/kernel/stacktrace.c | 3 +++
 arch/arm64/kvm/hyp/nvhe/host.S | 9 ++-------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index a84e38d41d38..f346b4c66f1c 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -242,4 +242,7 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 
 	unwind(task, &state, consume_entry, cookie);
 }
+#else /* __KVM_NVHE_HYPERVISOR__ */
+DEFINE_PER_CPU(unsigned long [PAGE_SIZE/sizeof(long)], overflow_stack)
+	__aligned(16);
 #endif /* !__KVM_NVHE_HYPERVISOR__ */
diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
index 09b5254fb497..1cd2de4f039e 100644
--- a/arch/arm64/kvm/hyp/nvhe/host.S
+++ b/arch/arm64/kvm/hyp/nvhe/host.S
@@ -179,13 +179,8 @@ SYM_FUNC_END(__host_hvc)
 	b	hyp_panic
 
 .L__hyp_sp_overflow\@:
-	/*
-	 * 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
-	 * any unwinding here.
-	 */
-	ldr_this_cpu	x0, kvm_init_params + NVHE_INIT_STACK_HYP_VA, x1
-	mov	sp, x0
+	/* Switch to the overflow stack */
+	adr_this_cpu sp, overflow_stack + PAGE_SIZE, x0
 
 	b	hyp_panic_bad_stack
 	ASM_BUG()
-- 
2.36.0.rc2.479.g8af0fa9b8e-goog