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

[Vishal Annapurve]

On Wed, Feb 12, 2025 at 4:54 AM Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
>
> 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.

Ack, will fix it in the next version.

>
> > @@ -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.

Let me replace it with a more suitable arch specific <>_irq_enable()
function in the next version. Intention here is to just enable
interrupts.

>
> --
>   Kiryl Shutsemau / Kirill A. Shutemov