Re: [PATCH V4 2/4] x86/tdx: Route safe halt execution via tdx_safe_halt()

[Kirill A. Shutemov]

On Wed, Feb 12, 2025 at 12:07:45AM +0000, Vishal Annapurve wrote:
> 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. So "sti;hlt" sequence needs to
> be replaced with "TDCALL; raw_local_irq_enable()" for TDX VMs.

The last sentence is somewhat confusing.

Maybe drop it and add explanation that #VE handler doesn't have info about
STI shadow, enables interrupts before TDCALL which can lead to missed
wakeup events.

> @@ -409,6 +410,12 @@ void __cpuidle tdx_safe_halt(void)
>  		WARN_ONCE(1, "HLT instruction emulation failed\n");
>  }
>  
> +static void __cpuidle tdx_safe_halt(void)
> +{
> +	tdx_halt();
> +	raw_local_irq_enable();

What is justification for raw_? Why local_irq_enable() is not enough?

To very least, it has to be explained.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov