linux-kernel - Re: [RFC PATCH 03/21] x86/virt/tdx: Add SEAMCALL wrapper tdh_mem_page

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Message-ID: <aAtUwfH30tqx92J6@yzhao56-desk.sh.intel.com>
Date: Fri, 25 Apr 2025 17:24:17 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
CC: <pbonzini@...hat.com>, <seanjc@...gle.com>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>, <x86@...nel.org>,
	<rick.p.edgecombe@...el.com>, <dave.hansen@...el.com>,
	<kirill.shutemov@...el.com>, <tabba@...gle.com>, <ackerleytng@...gle.com>,
	<quic_eberman@...cinc.com>, <michael.roth@....com>, <david@...hat.com>,
	<vannapurve@...gle.com>, <vbabka@...e.cz>, <jroedel@...e.de>,
	<thomas.lendacky@....com>, <pgonda@...gle.com>, <zhiquan1.li@...el.com>,
	<fan.du@...el.com>, <jun.miao@...el.com>, <ira.weiny@...el.com>,
	<isaku.yamahata@...el.com>, <xiaoyao.li@...el.com>, <chao.p.peng@...el.com>
Subject: Re: [RFC PATCH 03/21] x86/virt/tdx: Add SEAMCALL wrapper
 tdh_mem_page_demote()

On Fri, Apr 25, 2025 at 03:25:12PM +0800, Binbin Wu wrote:
> 
> 
> On 4/25/2025 3:17 PM, Yan Zhao wrote:
> > On Fri, Apr 25, 2025 at 03:12:32PM +0800, Binbin Wu wrote:
> > > 
> > > On 4/24/2025 11:04 AM, Yan Zhao wrote:
> > > > From: Xiaoyao Li <xiaoyao.li@...el.com>
> > > > 
> > > > Add a wrapper tdh_mem_page_demote() to invoke SEAMCALL TDH_MEM_PAGE_DEMOTE
> > > > to demote a huge leaf entry to a non-leaf entry in S-EPT. Currently, the
> > > > TDX module only supports demotion of a 2M huge leaf entry. After a
> > > > successful demotion, the old 2M huge leaf entry in S-EPT is replaced with a
> > > > non-leaf entry, linking to the newly-added page table page. The newly
> > > > linked page table page then contains 512 leaf entries, pointing to the 2M
> > > 2M or 4K?
> > The 512 leaf entries point to 2M guest private pages together,
> If this, it should be 2M range, since it's not a huge page after demotion.
> Also, the plural "pages" is confusing.
Ah, indeed, plural "pages" is confiusing :)
Maybe below is better:

The newly linked page table now contains 512 leaf entries, each pointing to a 4K
guest private page within the 2M range.


> >   each pointing to
> > 4K.
> > 
> > > > guest private pages.
>