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

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Message-ID: <a578e3b5-9fd3-4f69-943f-9415f4047e19@intel.com>
Date: Tue, 26 Aug 2025 10:18:17 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Kai Huang <kai.huang@...el.com>
Cc: 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,
 pbonzini@...hat.com, 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 8/26/25 10:10, Sean Christopherson wrote:
>> +void tdx_cpu_flush_cache_for_kexec(void)
>> +{
>> +	lockdep_assert_preemption_disabled();
>> +
>> +	if (!this_cpu_read(cache_state_incoherent))
>> +		return;
>> +
> 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 🙂

You mean as opposed to #ifdef'ing it out?

Looking at the code again, I completely agree in concept. The connection
between TDX, kexec and 'cache_state_incoherent' is totally opaque.