linux-kernel - Re: [PATCH 1/1] x86/tdx: Route safe halt execution via tdx_safe

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Message-ID: <sbcyntzl2z3egouaysbd7ua3obldyl7ukpwvy5jehnq5vcke7p@i27u43q7x2rb>
Date: Wed, 29 Jan 2025 12:37:27 +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
Subject: Re: [PATCH 1/1] x86/tdx: Route safe halt execution via tdx_safe_halt

On Tue, Jan 28, 2025 at 09:36:52PM +0000, Vishal Annapurve wrote:
> Direct HLT instruction execution causes #VEs for TDX VMs which is routed
> to hypervisor via tdvmcall. This process renders HLT instruction
> execution inatomic, so any preceeding instructions like STI/MOV SS will
> end up enabling interrupts before the HLT instruction is routed to the
> hypervisor. This creates scenarios where interrupts could land during
> HLT instruction emulation without aborting halt operation leading to
> idefinite halt wait times.
> 
> x86_idle is already upgraded to invoke tdx_safe_halt to avoid such
> scenarios, but it didn't cover pvnative_safe_halt which can be invoked
> using raw_safe_halt from call sites like acpi_safe_halt (acpi_pm
> subsystem). This patch upgrades the safe_halt executions to use
> tdx_safe_halt.

The question is why acpi_safe_halt() is ever called.

It only supposed to be called if the CPU supports C-states. See
pr->flags.power check in acpi_processor_power_init().

pr->flags.power is zero for me.

Maybe your BIOS is broken and enumerates C-states. I don't see how
C-states make sense for VMs.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov