linux-kernel - Re: [PATCH v15 22/23] x86/mce: Improve error log of kernel space TDX #MC due to erratum

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Message-ID: <b517f60a-728f-468d-989c-2669c7e71b91@intel.com>
Date:   Tue, 5 Dec 2023 12:49:46 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>, "Huang, Kai" <kai.huang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Brown, Len" <len.brown@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "nik.borisov@...e.com" <nik.borisov@...e.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Luck, Tony" <tony.luck@...el.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "sagis@...gle.com" <sagis@...gle.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v15 22/23] x86/mce: Improve error log of kernel space TDX
 #MC due to erratum

On 12/5/23 12:41, Borislav Petkov wrote:
> On Tue, Dec 05, 2023 at 08:33:14PM +0000, Huang, Kai wrote:
>> Yes I understand what you said.  My point is X86_FEATURE_TDX doesn't suit
>> because when it is set, the kernel actually hasn't done any enabling work yet
>> thus TDX is not available albeit the X86_FEATURE_TDX is set.
> You define a X86_FEATURE flag. You set it *when* TDX is available and
> enabled. Then you query that flag. This is how synthetic flags work.
> 
> In your patchset, when do you know that TDX is enabled? Point me to the
> code place pls.

TDX can be "ready" in a couple of different ways:

1. The module is there and running SEAMCALLS (tdx_platform_enabled())
2. The module is initialized and ready to run guests.  This happens
   after init_tdmrs() and init_tdx_module() return success.

#1 is known at boot.
#2 doesn't happen until just before KVM runs the first TDX guest.
Here's the patch for #2:

> https://lore.kernel.org/all/566ff8b05090c935d980d5ace3389d31c7cce7df.1699527082.git.kai.huang@intel.com/