linux-kernel - Re: [RFC v2-fix 1/1] x86/traps: Add #VE support for TDX guest

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Date:   Tue, 18 May 2021 08:56:06 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Tony Luck <tony.luck@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC v2-fix 1/1] x86/traps: Add #VE support for TDX guest

On 5/18/21 8:45 AM, Andi Kleen wrote:
> 
> On 5/18/2021 8:11 AM, Dave Hansen wrote:
>> On 5/17/21 5:09 PM, Kuppuswamy Sathyanarayanan wrote:
>>> After TDGETVEINFO #VE could happen in theory (e.g. through an NMI),
>>> although we don't expect it to happen because we don't expect NMIs to
>>> trigger #VEs. Another case where they could happen is if the #VE
>>> exception panics, but in this case there are no guarantees on anything
>>> anyways.
>> This implies: "we do not expect any NMI to do MMIO".  Is that true?  Why?
> 
> Only drivers that are not supported in TDX anyways could do it (mainly
> watchdog drivers)

No APIC access either?

Also, shouldn't we have at least a:

	WARN_ON_ONCE(in_nmi());

if we don't expect (or handle well) #VE in NMIs?