linux-kernel - Re: [PATCH 1/5] x86/virt/tdx: Rename _offset to _member for TD_SYSINFO

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Message-ID: <9aac71bcec5956177c288e4d0d0e6427c0986877.camel@intel.com>
Date: Mon, 6 May 2024 11:34:21 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Edgecombe,
 Rick P" <rick.p.edgecombe@...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 1/5] x86/virt/tdx: Rename _offset to _member for
 TD_SYSINFO_MAP() macro

On Fri, 2024-05-03 at 00:07 +0000, Edgecombe, Rick P wrote:
> On Sat, 2024-03-02 at 00:20 +1300, Kai Huang wrote:
> > TD_SYSINFO_MAP() macro actually takes the member of the 'struct
> > tdx_tdmr_sysinfo' as the second argument and uses the offsetof() to
> > calculate the offset for that member.
> > 
> > Rename the macro argument _offset to _member to reflect this.
> 
> The KVM patches will want to use this macro. The fact that it is misnamed will
> percolate into the KVM code if it is not updated before it gets wider callers.
> (This is a reason why this is good change from KVM's perspective).
> 
> See the KVM code below:
> 
> #define TDX_INFO_MAP(_field_id, _member)		\
> 	TD_SYSINFO_MAP(_field_id, struct st, _member)
> 
> 	struct tdx_metadata_field_mapping st_fields[] = {
> 		TDX_INFO_MAP(NUM_CPUID_CONFIG, num_cpuid_config),
> 		TDX_INFO_MAP(TDCS_BASE_SIZE, tdcs_base_size),
> 		TDX_INFO_MAP(TDVPS_BASE_SIZE, tdvps_base_size),
> 	};
> #undef TDX_INFO_MAP
> 
> #define TDX_INFO_MAP(_field_id, _member)			\
> 	TD_SYSINFO_MAP(_field_id, struct tdx_info, _member)
> 
> 	struct tdx_metadata_field_mapping fields[] = {
> 		TDX_INFO_MAP(FEATURES0, features0),
> 		TDX_INFO_MAP(ATTRS_FIXED0, attributes_fixed0),
> 		TDX_INFO_MAP(ATTRS_FIXED1, attributes_fixed1),
> 		TDX_INFO_MAP(XFAM_FIXED0, xfam_fixed0),
> 		TDX_INFO_MAP(XFAM_FIXED1, xfam_fixed1),
> 	};
> #undef TDX_INFO_MAP

I was thinking how to respond.  I guess your point is we can also mention
KVM will need to use this too so it's better to change it before it gets
wider callers.  But I don't think it is needed because if it is misnamed
now then we already have a justification to do it.

And technically, I don't think the argument name used in KVM actually has
anything to do with the argument name used in the TD_SYSINFO_MAP() macro
definition here.  What really matters is when they get used, we need to
pass the "real struct member": 

	struct whatever {
		u64 a;
		u16 b;
	};

	#define TDX_INFO_MAP_WHATEVER(_field_id, _xyz)	\
		TD_SYSINFO_MAP(_field_id, struct whatever, _xyz)

	const struct tdx_metadata_field_mapping fields[] = {
		TDX_INFO_MAP_WHATEVER(_FIELD_A, a),
		TDX_INFO_MAP_WHATEVER(_FIELD_B, b),
	};

No?