linux-kernel - Re: [PATCH v2 2/7] KVM: x86: Extract VMXON and EFER.SVME enablement to kernel

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Message-ID: <63935b64dea22cc7a1c938e5e9b6acaec2c10166.camel@intel.com>
Date: Fri, 19 Dec 2025 21:12:52 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>, "yilun.xu@...ux.intel.com"
	<yilun.xu@...ux.intel.com>
CC: "Gao, Chao" <chao.gao@...el.com>, "x86@...nel.org" <x86@...nel.org>,
	"kas@...nel.org" <kas@...nel.org>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "bp@...en8.de" <bp@...en8.de>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "linux-coco@...ts.linux.dev"
	<linux-coco@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Williams, Dan J" <dan.j.williams@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 2/7] KVM: x86: Extract VMXON and EFER.SVME enablement
 to kernel

On Fri, 2025-12-19 at 07:40 -0800, Sean Christopherson wrote:
> Kai, question for you (or anyone else that might know):
> 
> Is there any **need** for tdx_cpu_enable() and try_init_module_global() to run
> with IRQs disabled?  AFAICT, the lockdep_assert_irqs_disabled() checks added by
> commit 6162b310bc21 ("x86/virt/tdx: Add skeleton to enable TDX on demand") were
> purely because, _when the code was written_, KVM enabled virtualization via IPI
> function calls.
> 
> But by the time the KVM code landed upstream in commit fcdbdf63431c ("KVM: VMX:
> Initialize TDX during KVM module load"), that was no longer true, thanks to
> commit 9a798b1337af ("KVM: Register cpuhp and syscore callbacks when enabling
> hardware") setting the stage for doing everything from task context.

The other intention was to make tdx_cpu_enable() as IRQ safe, since it was
supposed to be able to be called by multiple in-kernel users but not just
KVM (i.e., also for TDX connect).

But right currently we don't need to call them with IRQ disabled.