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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Fri, 21 May 2021 12:22:21 -0700
Message-ID: <CAPcyv4i5a7ERZ8n=_Ucffx1cLru7C08xz3cB6X0iG+4yLTUYQQ@mail.gmail.com>
Subject: Re: [RFC v2-fix 1/1] x86/traps: Add #VE support for TDX guest
To:     Andi Kleen <ak@linux.intel.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Tony Luck <tony.luck@intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        Raj Ashok <ashok.raj@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Sean Christopherson <sean.j.christopherson@intel.com>
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On Tue, May 18, 2021 at 8:45 AM Andi Kleen <ak@linux.intel.com> 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)

What about apei_{read,write}() for ACPI error handling? Those are
called in NMI to do MMIO accesses. It's not just watchdog drivers.