linux-kernel - Re: [PATCH v4 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

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Date:   Wed, 31 Mar 2021 15:00:33 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andi Kleen <ak@...ux.intel.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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

On 3/31/21 2:53 PM, Sean Christopherson wrote:
> On Wed, Mar 31, 2021, Kuppuswamy Sathyanarayanan wrote:
>> Changes since v3:
>>  * WARN user if SEAM does not disable MONITOR/MWAIT instruction.
> Why bother?  There are a whole pile of features that are dictated by the TDX
> module spec.  MONITOR/MWAIT is about as uninteresting as it gets, e.g. absolute
> worst case scenario is the guest kernel crashes, whereas a lot of spec violations
> would compromise the security of the guest.

So, what should we do?  In the #VE handler:

	switch (exit_reason) {
	case SOMETHING_WE_HANDLE:
		blah();
		break;
		...
	default:
		pr_err("unhadled #VE, exit reason: %d\n", exit_reason);
		BUG_ON(1);
	}

?

Is this the *ONLY* one of these, or are we going to have another twenty?

If this is the only one, we might as well give a nice string error
message.  If there are twenty more, let's just dump the exit reason,
BUG() and move on with our lives.