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

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Message-ID: <6e839de0e66ac2a9a8af7fd78757b2ed1bffbca4.camel@intel.com>
Date: Fri, 3 May 2024 18:31:28 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Huang, Kai"
	<kai.huang@...el.com>
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 Fri, 2024-05-03 at 14:17 +1200, Huang, Kai wrote:
> 
> 
> 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.

Having one export would be nice. Yea, since the multiple field processing
version just loops anyway, doing it like you propose seems reasonable.