linux-kernel - Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

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Message-ID: <f5101cfa773a5dd89dd40ff9023024f4782b8123.camel@intel.com>
Date: Fri, 15 Aug 2025 00:00:50 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>
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Subject: Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX
 SEAMCALLs

On Thu, 2025-08-14 at 16:22 -0700, Sean Christopherson wrote:
> On Thu, Aug 14, 2025, Kai Huang wrote:
> > On Thu, 2025-08-14 at 11:00 -0700, Sean Christopherson wrote:
> > > > > > +	 */
> > > > > > +	tdx_cpu_flush_cache();
> > > > > 
> > > > > IIUC, this can be:
> > > > > 
> > > > > 	if (IS_ENABLED(CONFIG_KEXEC))
> > > > > 		tdx_cpu_flush_cache();
> > > > > 
> > > > 
> > > > No strong objection, just 2 cents. I bet !CONFIG_KEXEC && CONFIG_INTEL_TDX_HOST
> > > > kernels will be the minority. Seems like an opportunity to simplify the code.
> > > 
> > > Reducing the number of lines of code is not always a simplification.  IMO, not
> > > checking CONFIG_KEXEC adds "complexity" because anyone that reads the comment
> > > (and/or the massive changelog) will be left wondering why there's a bunch of
> > > documentation that talks about kexec, but no hint of kexec considerations in the
> > > code.
> > 
> > I think we can use 'kexec_in_progress', which is even better than
> > IS_ENABLED(CONFIG_KEXEC) IMHO.
> 
> I don't think that will accomplish what you want.  E.g. kvm-intel.ko is unloaded
> after doing TDX things, while kexec_in_progress=false, and then some time later
> a kexec is triggered.  In that case, stop_this_cpu() will still get stuck doing
> WBINVD.

Right.  Thanks.  Let me think more on this.

One minor thing is I think we should use IS_ENABLED(CONFIG_KEXEC_CORE)
instead.  Besides the CONFIG_KEXEC, there is another CONFIG_KEXEC_FILE,
and both of them select CONFIG_KEXEC_CORE.