linux-kernel - Re: [RFC PATCH v2 02/23] x86/virt/tdx: Add SEAMCALL wrapper tdh_mem_page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aRRAFhw11Dwcw7RG@yzhao56-desk.sh.intel.com>
Date: Wed, 12 Nov 2025 16:06:46 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Huang, Kai" <kai.huang@...el.com>
CC: "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>,
	"quic_eberman@...cinc.com" <quic_eberman@...cinc.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "Li, Xiaoyao" <xiaoyao.li@...el.com>, "Du, Fan"
	<fan.du@...el.com>, "Hansen, Dave" <dave.hansen@...el.com>,
	"david@...hat.com" <david@...hat.com>, "thomas.lendacky@....com"
	<thomas.lendacky@....com>, "vbabka@...e.cz" <vbabka@...e.cz>,
	"tabba@...gle.com" <tabba@...gle.com>, "michael.roth@....com"
	<michael.roth@....com>, "seanjc@...gle.com" <seanjc@...gle.com>, "Weiny, Ira"
	<ira.weiny@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>, "Peng,
 Chao P" <chao.p.peng@...el.com>, "ackerleytng@...gle.com"
	<ackerleytng@...gle.com>, "kas@...nel.org" <kas@...nel.org>, "Yamahata,
 Isaku" <isaku.yamahata@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Annapurve, Vishal" <vannapurve@...gle.com>,
	"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "Miao, Jun"
	<jun.miao@...el.com>, "zhiquan1.li@...el.com" <zhiquan1.li@...el.com>,
	"x86@...nel.org" <x86@...nel.org>, "pgonda@...gle.com" <pgonda@...gle.com>
Subject: Re: [RFC PATCH v2 02/23] x86/virt/tdx: Add SEAMCALL wrapper
 tdh_mem_page_demote()

On Tue, Nov 11, 2025 at 05:15:22PM +0800, Huang, Kai wrote:
> On Mon, 2025-09-01 at 17:08 +0800, Yan Zhao wrote:
> > > > Do not handle TDX_INTERRUPTED_RESTARTABLE because SEAMCALL
> > > > TDH_MEM_PAGE_DEMOTE does not check interrupts (including NMIs) for basic
> > > > TDX (with or without Dynamic PAMT).
> > > 
> > > The cover letter mentions that there is a new TDX module in planning, which
> > > disables the interrupt checking. I guess TDX module would need to have a
> > > interface to report the change, KVM then decides to enable huge page support or
> > > not for TDs?
> > Yes. But I guess detecting TDX module version or if it supports certain feature
> > is a generic problem. e.g., certain versions of TDX module have bugs in
> > zero-step mitigation and may block vCPU entering.
> > 
> > So, maybe it deserves a separate series?
> 
> Looking at the spec (TDX module ABI spec 348551-007US), is it enumerated via
> TDX_FEATURES0.ENHANCED_DEMOTE_INTERRUPTIBILITY?
Yes. I checked the unreleased TDX module code that enumerates this bit (starting
from version TDX_1.5.28.00.972). TDH.MEM.PAGE.DEMOTE will not return
TDX_INTERRUPTED_RESTARTABLE for L1 VMs.

>   5.4.25.3.9.
> 
>   Interruptibility
> 
>   If the TD is not partitioned (i.e., it has been configured with no L2 
>   VMs), and the TDX Module enumerates 
>   TDX_FEATURES0.ENHANCED_DEMOTE_INTERRUPTIBILITY as 1, TDH.MEM.PAGE.DEMOTE 
>   is not interruptible.
> 
> So if the decision is to not use 2M page when TDH_MEM_PAGE_DEMOTE can return
> TDX_INTERRUPTED_RESTARTABLE, maybe we can just check this enumeration in
> fault handler and always make mapping level as 4K?
Thanks for this info! I think this is a very good idea and the right direction.
If no objection, I'll update the code in this way.