linux-kernel - Re: [PATCH v6 04/10] x86/virt/tdx: Use dedicated struct members for PAMT entry sizes

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Message-ID: <67200770bea9b_bc69d2947d@dwillia2-xfh.jf.intel.com.notmuch>
Date: Mon, 28 Oct 2024 14:51:44 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Kai Huang <kai.huang@...el.com>, <dave.hansen@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <tglx@...utronix.de>, <bp@...en8.de>,
	<peterz@...radead.org>, <mingo@...hat.com>, <hpa@...or.com>,
	<dan.j.williams@...el.com>, <seanjc@...gle.com>, <pbonzini@...hat.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<rick.p.edgecombe@...el.com>, <isaku.yamahata@...el.com>,
	<adrian.hunter@...el.com>, <nik.borisov@...e.com>, <kai.huang@...el.com>
Subject: Re: [PATCH v6 04/10] x86/virt/tdx: Use dedicated struct members for
 PAMT entry sizes

Kai Huang wrote:
> Currently, the 'struct tdmr_sys_info_tdmr' which includes TDMR related
> fields defines the PAMT entry sizes for TDX supported page sizes (4KB,
> 2MB and 1GB) as an array:
> 
> 	struct tdx_sys_info_tdmr {
> 		...
> 		u16 pamt_entry_sizes[TDX_PS_NR];
> 	};
> 
> PAMT entry sizes are needed when allocating PAMTs for each TDMR.  Using
> the array to contain PAMT entry sizes reduces the number of arguments
> that need to be passed when calling tdmr_set_up_pamt().  It also makes
> the code pattern like below clearer:
> 
> 	for (pgsz = TDX_PS_4K; pgsz < TDX_PS_NR; pgsz++) {
> 		pamt_size[pgsz] = tdmr_get_pamt_sz(tdmr, pgsz,
> 					pamt_entry_size[pgsz]);
> 		tdmr_pamt_size += pamt_size[pgsz];
> 	}
> 
> However, the auto-generated metadata reading code generates a structure
> member for each field.  The 'global_metadata.json' has a dedicated field
> for each PAMT entry size, and the new 'struct tdx_sys_info_tdmr' looks
> like:
> 
> 	struct tdx_sys_info_tdmr {
> 		...
> 		u16 pamt_4k_entry_size;
> 		u16 pamt_2m_entry_size;
> 		u16 pamt_1g_entry_size;
> 	};
> 
> To prepare to use the auto-generated code, make the existing 'struct
> tdx_sys_info_tdmr' look like the generated one.  But when passing to
> tdmrs_set_up_pamt_all(), build a local array of PAMT entry sizes from
> the structure so the code to allocate PAMTs can stay the same.
> 
> Signed-off-by: Kai Huang <kai.huang@...el.com>

Makes sense to align with the autogenerated code to reduce maintenance/review
fatigue going forward.

Reviewed-by: Dan Williams <dan.j.williams@...el.com>