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

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Message-ID: <CALCETrVzdq7eQu6RfJd0+yuJ+Q9Q6NykVb+x_jiNwLW2-mrh0w@mail.gmail.com>
Date:   Mon, 29 Mar 2021 16:58:23 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        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>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

On Mon, Mar 29, 2021 at 4:42 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> 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.

Dare I ask about XSETBV?