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

From: "Huang, Kai" <kai.huang@intel.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: "Hansen, Dave" <dave.hansen@intel.com>,
	"seanjc@google.com" <seanjc@google.com>,
	"bp@alien8.de" <bp@alien8.de>, "x86@kernel.org" <x86@kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"kirill.shutemov@linux.intel.com"
	<kirill.shutemov@linux.intel.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	"jgross@suse.com" <jgross@suse.com>,
	"Yamahata, Isaku" <isaku.yamahata@intel.com>
Subject: Re: [PATCH 5/5] x86/virt/tdx: Export global metadata read infrastructure
Date: Fri, 3 May 2024 14:17:26 +1200	[thread overview]
Message-ID: <330c909a-4b96-4960-9cad-fd10e86c67b8@intel.com> (raw)
In-Reply-To: <affad906c557f251ab189770f5a45cd2087aca19.camel@intel.com>

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.