On Tue, Feb 25, 2025 at 12:47:03AM +0000, Vishal Annapurve wrote:
Direct HLT instruction execution causes #VEs for TDX VMs which is routed to hypervisor via TDCALL. If HLT is executed in STI-shadow, resulting #VE handler will enable interrupts before TDCALL is routed to hypervisor leading to missed wakeup events.
Current TDX spec doesn't expose interruptibility state information to allow #VE handler to selectively enable interrupts. To bypass this issue, TDX VMs need to replace "sti;hlt" execution with direct TDCALL followed by explicit interrupt flag update.
Commit bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests") prevented the idle routines from executing HLT instruction in STI-shadow. But it missed the paravirt routine which can be reached like this as an example: acpi_safe_halt() => raw_safe_halt() => arch_safe_halt() => irq.safe_halt() => pv_native_safe_halt()
I would rather use paravirt spinlock example. It is less controversial. I still see no point in ACPI cpuidle be a thing in TDX guests.
To reliably handle arch_safe_halt() for TDX VMs, introduce explicit dependency on CONFIG_PARAVIRT and override paravirt halt()/safe_halt() routines with TDX-safe versions that execute direct TDCALL and needed interrupt flag updates. Executing direct TDCALL brings in additional benefit of avoiding HLT related #VEs altogether.
Cc: stable@vger.kernel.org Fixes: bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests") Signed-off-by: Vishal Annapurve vannapurve@google.com
Reviewed-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com