linux-kernel - Re: [RFC v1 05/26] x86/traps: Add #VE support for TDX guest

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Date:   Sun, 14 Feb 2021 11:33:20 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        LKML <linux-kernel@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC v1 05/26] x86/traps: Add #VE support for TDX guest

On Fri, Feb 12, 2021 at 01:48:36PM -0800, Dave Hansen wrote:
> On 2/12/21 1:47 PM, Andy Lutomirski wrote:
> >> What about adding a property to the TD, e.g. via a flag set during TD creation,
> >> that controls whether unaccepted accesses cause #VE or are, for all intents and
> >> purposes, fatal?  That would allow Linux to pursue treating EPT #VEs for private
> >> GPAs as fatal, but would give us a safety and not prevent others from utilizing
> >> #VEs.
> > That seems reasonable.
> 
> Ditto.
> 
> We first need to double check to see if the docs are right, though.

I confirmed with the TDX module owners that #VE can only happen for:
- unaccepted pages
- instructions like MSR access or CPUID
- specific instructions that are no in the syscall gap

Also if there are future asynchronous #VEs they would only happen
with IF=1, which would also protect the gap.

So no need to make #VE an IST.

-Andi