linux-kernel - Re: [PATCH v7 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

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Message-ID: <aK3xH4MGv9ZMxhyY@google.com>
Date: Tue, 26 Aug 2025 10:38:39 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Kai Huang <kai.huang@...el.com>, dave.hansen@...el.com, bp@...en8.de, 
	tglx@...utronix.de, peterz@...radead.org, mingo@...hat.com, hpa@...or.com, 
	thomas.lendacky@....com, x86@...nel.org, kas@...nel.org, 
	rick.p.edgecombe@...el.com, dwmw@...zon.co.uk, linux-kernel@...r.kernel.org, 
	kvm@...r.kernel.org, reinette.chatre@...el.com, isaku.yamahata@...el.com, 
	dan.j.williams@...el.com, ashish.kalra@....com, nik.borisov@...e.com, 
	chao.gao@...el.com, sagis@...gle.com, farrah.chen@...el.com, 
	Binbin Wu <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH v7 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

On Tue, Aug 26, 2025, Paolo Bonzini wrote:
> On Tue, Aug 26, 2025 at 7:10 PM Sean Christopherson <seanjc@...gle.com> wrote:
> > Can you add a comment here to explain why this is done even if the kernel doesn't
> > support kexec?  I've no objection to the superfluous flushing, but I've spent far
> > too much time deciphering old commits where the changelog says one thing and the
> > code does something else with no explanation.  I don't want to be party to such
> > crimes :-)
> 
> I asked on the review for v6 to make this conditional on CONFIG_KEXEC_CORE
> with a stub; Kai said he'd rather not and I acquiesced, but now it looks
> like we're going to need a v8 just for this comment or to follow that
> suggestion of mine, which I still prefer to a comment.

FWIW, I also prefer conditioning the flush with an #ifdef (we could even have
both an #ifdef and a comment), but it's not a hill I'll die on.