[PATCH V3 2/2] x86/tdx: Emit warning if IRQs are enabled during HLT #VE handling

[Vishal Annapurve <vannapurve@google.com>]

Direct HLT instruction execution causes #VEs for TDX VMs which is routed
to hypervisor via TDCALL. safe_halt() routines execute HLT in STI-shadow
so IRQs need to remain disabled until the TDCALL to ensure that pending
IRQs are correctly treated as wake events.

Emit warning and fail emulation if IRQs are enabled during HLT #VE handling
to avoid running into scenarios where IRQ wake events are lost resulting in
indefinite HLT execution times.

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>@linux.intel.com>
Signed-off-by: Vishal Annapurve <vannapurve@google.com>
---
 arch/x86/coco/tdx/tdx.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 5e68758666a4..ed6738ea225c 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -393,6 +393,11 @@ static int handle_halt(struct ve_info *ve)
 {
 	const bool irq_disabled = irqs_disabled();
 
+	if (!irq_disabled) {
+		WARN_ONCE(1, "HLT instruction emulation unsafe with irqs enabled\n");
+		return -EIO;
+	}
+
 	if (__halt(irq_disabled))
 		return -EIO;
 
-- 
2.48.1.502.g6dc24dfdaf-goog