linux-kernel - Re: [PATCH V4 2/4] x86/tdx: Route safe halt execution via tdx_safe

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Message-ID: <CAGtprH9OVVMXLyPnKXZ+K=S7XuPePHLwco0sXV-irGVj-SCbkQ@mail.gmail.com>
Date: Thu, 13 Feb 2025 09:33:20 -0800
From: Vishal Annapurve <vannapurve@...gle.com>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, pbonzini@...hat.com, 
	seanjc@...gle.com, erdemaktas@...gle.com, ackerleytng@...gle.com, 
	jxgao@...gle.com, sagis@...gle.com, oupton@...gle.com, pgonda@...gle.com, 
	dave.hansen@...ux.intel.com, linux-coco@...ts.linux.dev, 
	chao.p.peng@...ux.intel.com, isaku.yamahata@...il.com, 
	sathyanarayanan.kuppuswamy@...ux.intel.com, stable@...r.kernel.org
Subject: Re: [PATCH V4 2/4] x86/tdx: Route safe halt execution via tdx_safe_halt()

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