linux-kernel - Re: [PATCH 5/9] x86/virt/tdx: Move field mapping table of getting TDMR info to function local

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Date: Tue, 18 Jun 2024 23:44:34 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "nik.borisov@...e.com" <nik.borisov@...e.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "Hansen, Dave"
	<dave.hansen@...el.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>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>, "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH 5/9] x86/virt/tdx: Move field mapping table of getting
 TDMR info to function local

On Tue, 2024-06-18 at 14:47 +0300, Nikolay Borisov wrote:
> 
> On 16.06.24 г. 15:01 ч., Kai Huang wrote:
> > For now the kernel only reads "TD Memory Region" (TDMR) related global
> > metadata fields to a 'struct tdx_tdmr_sysinfo' for initializing the TDX
> > module.  The kernel populates the relevant metadata fields into the
> > structure using a "field mapping table" of metadata field IDs and the
> > structure members.
> > 
> > Currently the scope of this "field mapping table" is the entire C file.
> > Future changes will need to read more global metadata fields that will
> > be organized in other structures and use this kind of field mapping
> > tables for other structures too.
> > 
> > Move the field mapping table to the function local to limit its scope so
> > that the same name can also be used by other functions.
> 
> nit: I think all of this could be condensed simply to :
> 
> "The mapping table is only used by foo() so move it there, no functional 
> changes". The consideration for future usage seems somewhat moot with 
> respect to such a trivial change. 
> 

Without future usage I am not sure whether it is worth to do such change,
so I would at least keep the future usage part.

And to explain "future usage", I think it would be helpful to have some
background text here.  So I tend to keep the current way.  But I am open
on this if other people have comments.

> In any case:
> 
> Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>

Thanks!

> 
> 
> > 
> > Signed-off-by: Kai Huang <kai.huang@...el.com>
> > ---
> >   arch/x86/virt/vmx/tdx/tdx.c | 18 +++++++++---------
> >   1 file changed, 9 insertions(+), 9 deletions(-)
> > 
> > diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> > index c68fbaf4aa15..fad42014ca37 100644
> > --- a/arch/x86/virt/vmx/tdx/tdx.c
> > +++ b/arch/x86/virt/vmx/tdx/tdx.c
> > @@ -322,17 +322,17 @@ static int stbuf_read_sysmd_multi(const struct field_mapping *fields,
> >   #define TD_SYSINFO_MAP_TDMR_INFO(_field_id, _member)	\
> >   	TD_SYSINFO_MAP(_field_id, struct tdx_tdmr_sysinfo, _member)
> >   
> > -/* Map TD_SYSINFO fields into 'struct tdx_tdmr_sysinfo': */
> > -static const struct field_mapping fields[] = {
> > -	TD_SYSINFO_MAP_TDMR_INFO(MAX_TDMRS,		max_tdmrs),
> > -	TD_SYSINFO_MAP_TDMR_INFO(MAX_RESERVED_PER_TDMR, max_reserved_per_tdmr),
> > -	TD_SYSINFO_MAP_TDMR_INFO(PAMT_4K_ENTRY_SIZE,    pamt_entry_size[TDX_PS_4K]),
> > -	TD_SYSINFO_MAP_TDMR_INFO(PAMT_2M_ENTRY_SIZE,    pamt_entry_size[TDX_PS_2M]),
> > -	TD_SYSINFO_MAP_TDMR_INFO(PAMT_1G_ENTRY_SIZE,    pamt_entry_size[TDX_PS_1G]),
> > -};
> > -
> >   static int get_tdx_tdmr_sysinfo(struct tdx_tdmr_sysinfo *tdmr_sysinfo)
> >   {
> > +	/* Map TD_SYSINFO fields into 'struct tdx_tdmr_sysinfo': */
> > +	static const struct field_mapping fields[] = {
> > +		TD_SYSINFO_MAP_TDMR_INFO(MAX_TDMRS,		max_tdmrs),
> > +		TD_SYSINFO_MAP_TDMR_INFO(MAX_RESERVED_PER_TDMR, max_reserved_per_tdmr),
> > +		TD_SYSINFO_MAP_TDMR_INFO(PAMT_4K_ENTRY_SIZE,    pamt_entry_size[TDX_PS_4K]),
> > +		TD_SYSINFO_MAP_TDMR_INFO(PAMT_2M_ENTRY_SIZE,    pamt_entry_size[TDX_PS_2M]),
> > +		TD_SYSINFO_MAP_TDMR_INFO(PAMT_1G_ENTRY_SIZE,    pamt_entry_size[TDX_PS_1G]),
> > +	};
> > +
> >   	/* Populate 'tdmr_sysinfo' fields using the mapping structure above: */
> >   	return stbuf_read_sysmd_multi(fields, ARRAY_SIZE(fields), tdmr_sysinfo);
> >   }