linux-kernel - Re: [PATCH v2 06/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX TD creation

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Message-ID: <1e1975a134b401c506eb5c4d0f093ce1e286d032.camel@intel.com>
Date: Tue, 12 Nov 2024 21:21:57 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "Hansen, Dave"
	<dave.hansen@...el.com>, "seanjc@...gle.com" <seanjc@...gle.com>
CC: "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>, "Yao,
 Yuan" <yuan.yao@...el.com>, "Huang, Kai" <kai.huang@...el.com>,
	"binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>, "Li, Xiaoyao"
	<xiaoyao.li@...el.com>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "tony.lindgren@...ux.intel.com"
	<tony.lindgren@...ux.intel.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Zhao, Yan Y" <yan.y.zhao@...el.com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v2 06/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX TD
 creation

On Tue, 2024-11-12 at 12:17 -0800, Dave Hansen wrote:
> On 10/30/24 12:00, Rick Edgecombe wrote:
> > +u64 tdh_mng_create(u64 tdr, u64 hkid)
> > +{
> > +	struct tdx_module_args args = {
> > +		.rcx = tdr,
> > +		.rdx = hkid,
> > +	};
> > +	clflush_cache_range(__va(tdr), PAGE_SIZE);
> > +	return seamcall(TDH_MNG_CREATE, &args);
> > +}
> > +EXPORT_SYMBOL_GPL(tdh_mng_create);
> 
> I'd _prefer_ that this explain why the clflush is there.

How about:
/*
 * The TDX module exposes a CLFLUSH_BEFORE_ALLOC bit to specify whether
 * a CLFLUSH of pages is required before handing them to the TDX module.
 * Be conservative and make the code simpler by doing the CLFLUSH 
 * unconditionally.
 */

> 
> The other goofy thing here is why it's getting a physical address passed
> in.  It's my old 32-bit paranoia kicking in, but everything that has a
> valid virtual address _also_ has a valid physical address.  The inverse
> is not true, though.  So I like to keep things as pointers as long as
> possible.

Ok, seems reasonable.