linux-kernel - Re: [PATCH 5/5] x86/virt/tdx: Export global metadata read infrastructure

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Date: Fri, 3 May 2024 14:17:26 +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>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "Hansen, Dave" <dave.hansen@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org"
	<x86@...nel.org>, "peterz@...radead.org" <peterz@...radead.org>,
	"hpa@...or.com" <hpa@...or.com>, "mingo@...hat.com" <mingo@...hat.com>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "jgross@...e.com" <jgross@...e.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>
Subject: Re: [PATCH 5/5] x86/virt/tdx: Export global metadata read
 infrastructure

On 3/05/2024 12:21 pm, Edgecombe, Rick P wrote:
> On Sat, 2024-03-02 at 00:20 +1300, Kai Huang wrote:
>> KVM will need to read a bunch of non-TDMR related metadata to create and
>> run TDX guests.  Export the metadata read infrastructure for KVM to use.
>>
>> Specifically, export two helpers:
>>
>> 1) The helper which reads multiple metadata fields to a buffer of a
>>     structure based on the "field ID -> structure member" mapping table.
>>
>> 2) The low level helper which just reads a given field ID.
>>
> Could 2 be a static inline in a helper, and then only have one export?

I assume you were thinking about making 2) call the 1), so we don't need 
to export 2).

This is not feasible due to:

a). 1) must 'struct tdx_metadata_field_mapping' table as input, and for 
that we need to ues the TDX_SYSINFO_MAP() macro to define a structure 
for just one 'u64' and define a 'struct tdx_metadata_field_mapping' 
table which only has one element for that.

b). TDX_SYSINFO_MAP() macro actually doesn't support taking a metadata 
field "variable", but can only support using the name of the metadata field.

However we can try to make 1) as a wrapper of 2).  But this would 
require some change to the patch 4.

I'll reply separately to patch 4 and you can take a look whether that is 
better.