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: <9b221937-42df-4381-b79f-05fb41155f7a@intel.com>
Date:   Mon, 4 Dec 2023 14:04:56 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Huang, Kai" <kai.huang@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "Luck, Tony" <tony.luck@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "nik.borisov@...e.com" <nik.borisov@...e.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "sagis@...gle.com" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "bp@...en8.de" <bp@...en8.de>, "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "Gao, Chao" <chao.gao@...el.com>
Subject: Re: [PATCH v15 22/23] x86/mce: Improve error log of kernel space TDX
 #MC due to erratum

On 12/4/23 13:00, Huang, Kai wrote:
>> tl;dr: I think even looking a #MC on the PAMT after the kvm module is
>> removed is a fool's errand.
> Sorry I wasn't clear enough.  KVM actually turns off VMX when it destroys the
> last VM, so the KVM module doesn't need to be removed to turn off VMX.  I used
> "KVM can be unloaded" as an example to explain the PAMT can be working when VMX
> is off.

Can't we just fix this by having KVM do an "extra" hardware_enable_all()
before initializing the TDX module?  It's not wrong to say that TDX is a
KVM user.  If KVm wants 'kvm_usage_count' to go back to 0, it can shut
down the TDX module.  Then there's no PAMT to worry about.

The shutdown would be something like:

	1. TDX module shutdown
	2. Deallocate/Convert PAMT
	3. vmxoff

Then, no SEAMCALL failure because of vmxoff can cause a PAMT-induced #MC
to be missed.