linux-kernel - Re: [PATCH v2 16/25] KVM: TDX: Get system-wide info about TDX module on initialization

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Message-ID: <ZySPK71RlFqPfkmU@tlindgre-MOBL1>
Date: Fri, 1 Nov 2024 10:19:55 +0200
From: Tony Lindgren <tony.lindgren@...ux.intel.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: Binbin Wu <binbin.wu@...ux.intel.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>, pbonzini@...hat.com,
	seanjc@...gle.com, yan.y.zhao@...el.com, isaku.yamahata@...il.com,
	kai.huang@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, reinette.chatre@...el.com,
	Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [PATCH v2 16/25] KVM: TDX: Get system-wide info about TDX module
 on initialization

On Thu, Oct 31, 2024 at 10:27:11PM +0800, Xiaoyao Li wrote:
> On 10/31/2024 5:37 PM, Tony Lindgren wrote:
> > On Thu, Oct 31, 2024 at 05:23:57PM +0800, Xiaoyao Li wrote:
> > > here it is to initialize the configurable CPUID bits that get reported to
> > > userspace. Though TDX module doesn't allow them to be set in TD_PARAM for
> > > KVM_TDX_INIT_VM, they get set to 0xff because KVM reuse these bits
> > > EBX[23:16] as the interface for userspace to configure GPAW of TD guest
> > > (implemented in setup_tdparams_eptp_controls() in patch 19). That's why they
> > > need to be set as all-1 to allow userspace to configure.
> > > 
> > > And the comment above it is wrong and vague. we need to change it to
> > > something like
> > > 
> > > 	/*
> > >           * Though TDX module doesn't allow the configuration of guest
> > >           * phys addr bits (EBX[23:16]), KVM uses it as the interface for
> > >           * userspace to configure the GPAW. So need to report these bits
> > >           * as configurable to userspace.
> > >           */
> > 
> > That sounds good to me.
> > 
> > Hmm so care to check if we can also just leave out another "old module"
> > comment in tdx_read_cpuid()?
> 
> That one did relate to old module, the module that without
> TDX_CONFIG_FLAGS_MAXGPA_VIRT reported in tdx_feature0.

OK thanks for checking.

> I will sent an follow up patch to complement the handling if TDX module
> supports TDX_CONFIG_FLAGS_MAXGPA_VIRT.

OK

Regards,

Tony