linux-kernel - Re: [PATCH 04/16] KVM: x86/mmu: Add address conversion functions for TDX shared bit of GPA

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Date: Thu, 16 May 2024 12:25:51 +1200
From: "Huang, Kai" <kai.huang@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"seanjc@...gle.com" <seanjc@...gle.com>
CC: "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, "sagis@...gle.com"
	<sagis@...gle.com>, "Aktas, Erdem" <erdemaktas@...gle.com>,
	"dmatlack@...gle.com" <dmatlack@...gle.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/16] KVM: x86/mmu: Add address conversion functions for
 TDX shared bit of GPA



On 16/05/2024 12:19 pm, Edgecombe, Rick P wrote:
> On Thu, 2024-05-16 at 12:12 +1200, Huang, Kai wrote:
>>
>> I don't have strong objection if the use of kvm_gfn_shared_mask() is
>> contained in smaller areas that truly need it.  Let's discuss in
>> relevant patch(es).
>>
>> However I do think the helpers like below makes no sense (for SEV-SNP):
>>
>> +static inline bool kvm_is_private_gpa(const struct kvm *kvm, gpa_t gpa)
>> +{
>> +       gfn_t mask = kvm_gfn_shared_mask(kvm);
>> +
>> +       return mask && !(gpa_to_gfn(gpa) & mask);
>> +}
> 
> You mean the name? SNP doesn't have a concept of "private GPA" IIUC. The C bit
> is more like an permission bit. So SNP doesn't have private GPAs, and the
> function would always return false for SNP. So I'm not sure it's too horrible.

Hmm.. Why SNP doesn't have private GPAs?  They are crypto-protected and 
KVM cannot access directly correct?

> 
> If it's the name, can you suggest something?

The name make sense, but it has to reflect the fact that a given GPA is 
truly private (crypto-protected, inaccessible to KVM).