linux-kernel - Re: [PATCH v3 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

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Message-ID: <YGJl93hlKngWLGwz@google.com>
Date:   Mon, 29 Mar 2021 23:42:47 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        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 v3 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

On Mon, Mar 29, 2021, Kuppuswamy, Sathyanarayanan wrote:
> 
> 
> On 3/29/21 4:23 PM, Andy Lutomirski wrote:
> > 
> > > On Mar 29, 2021, at 4:17 PM, Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com> wrote:
> > > 
> > > In non-root TDX guest mode, MWAIT, MONITOR and WBINVD instructions
> > > are not supported. So handle #VE due to these instructions
> > > appropriately.
> > 
> > Is there something I missed elsewhere in the code that checks CPL?
> We don't check for CPL explicitly. But if we are reaching here, then we
> executing these instructions with wrong CPL.

No, if these instructions take a #VE then they were executed at CPL=0.  MONITOR
and MWAIT will #UD without VM-Exit->#VE.  Same for WBINVD, s/#UD/#GP.