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

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Message-ID: <ljdzupgyl2am4qgvirwpdonwuzwjaysemu43icrzxjt5olr3yx@dldbi5tqwhjh>
Date: Wed, 12 Feb 2025 14:54:17 +0200
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Vishal Annapurve <vannapurve@...gle.com>
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 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