linux-kernel - Re: [PATCH v4 6/6] KVM: x86: Refactor __kvm_emulate

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Message-ID: <Z1ier7QAy9qj7x4V@google.com>
Date: Tue, 10 Dec 2024 12:03:59 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Tom Lendacky <thomas.lendacky@....com>, 
	Binbin Wu <binbin.wu@...ux.intel.com>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	Kai Huang <kai.huang@...el.com>, Xiaoyao Li <xiaoyao.li@...el.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v4 6/6] KVM: x86: Refactor __kvm_emulate_hypercall() into
 a macro

On Tue, Dec 10, 2024, Paolo Bonzini wrote:
> On 11/28/24 09:38, Adrian Hunter wrote:
> > 
> > For TDX, there is an RFC relating to using descriptively
> > named parameters instead of register names for tdh_vp_enter():
> > 
> > 	https://lore.kernel.org/all/fa817f29-e3ba-4c54-8600-e28cf6ab1953@intel.com/
> > 
> > Please do give some feedback on that approach.  Note we
> > need both KVM and x86 maintainer approval for SEAMCALL
> > wrappers like tdh_vp_enter().
> > 
> > As proposed, that ends up with putting the values back into
> > vcpu->arch.regs[] for __kvm_emulate_hypercall() which is not
> > pretty:
> 
> If needed we can revert this patch, it's not a big problem.

I don't care terribly about the SEAMCALL interfaces.  I have opinions on what
would I think would be ideal, but I can live with whatever.

What I do deeply care about though is consistency within KVM, across vendors and
VM flavors.  And that means that guest registers absolutely need to be captured in
vcpu->arch.regs[].  TDX already requires too much special cased code in KVM, there
is zero reason to make TDX even more different and thus more difficult to maintain.