linux-kernel - Re: [PATCH 4/5] x86/virt/tdx: Support global metadata read for all element sizes

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Message-ID: <0c72ebbaa1add993bad258153304a4d6eac59456.camel@intel.com>
Date: Mon, 6 May 2024 10:59:15 +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 4/5] x86/virt/tdx: Support global metadata read for all
 element sizes

On Fri, 2024-05-03 at 18:32 +0000, Edgecombe, Rick P wrote:
> On Fri, 2024-05-03 at 12:26 +0000, Huang, Kai wrote:
> > 
> > To resolve this once for all, extend the existing metadata reading code
> > to provide a generic metadata read infrastructure which supports reading
> > all 8/16/32/64 bits element sizes.
> 
> I think the key point is that it is actually simpler to support all field types
> then only 16 and 64.

How about add below to the end of the changelog:

The metadata field ID encodes the element size.  The TDH.SYS.RD SEAMCALL
always returns 64-bit metadata data regardless of the true element size of
the metadata field.  The current function to read 16-bit metadata fields
checks the element size encoded in the field ID is indeed 16-bits.

Change that function to just covert the data from the SEAMCALL to the size
encoded in the metadata field ID to provide a function which supports all
element sizes.  It's actually simpler to support reading all element sizes
in one function rather than providing two functions to read 16 and 64 bits
elements respectively.