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

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Date:   Tue, 30 Mar 2021 15:14:10 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andi Kleen <ak@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.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, Andy Lutomirski wrote:
> 
> > On Mar 29, 2021, at 7:04 PM, Andi Kleen <ak@...ux.intel.com> wrote:
> > 
> > 
> >> 
> >>> 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?
> > 
> > XGETBV does not cause a #VE, it just works normally. The guest has full
> > AVX capabilities.
> > 
> 
> X *SET* BV

Heh, XSETBV also works normally, relative to the features enumerated in CPUID.
XSAVES/XRSTORS support is fixed to '1' in the virtual CPU model.  A subset of
the features managed by XSAVE can be hidden by the VMM, but attempting to enable
unsupported features will #GP (either from hardware or injected by TDX Module),
not #VE.