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Date:   Tue, 30 Mar 2021 08:00:48 -0700
From:   Andi Kleen <ak@linux.intel.com>
To:     Xiaoyao Li <xiaoyao.li@intel.com>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Raj Ashok <ashok.raj@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD
Message-ID: <20210330150048.GB1285835@tassilo.jf.intel.com>
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On Tue, Mar 30, 2021 at 12:56:41PM +0800, Xiaoyao Li wrote:
> On 3/27/2021 8:18 AM, Kuppuswamy Sathyanarayanan wrote:
> > In non-root TDX guest mode, MWAIT, MONITOR and WBINVD instructions
> > are not supported. So handle #VE due to these instructions as no ops.
> > 
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> > Reviewed-by: Andi Kleen <ak@linux.intel.com>
> > ---
> > 
> > Changes since previous series:
> >   * Suppressed MWAIT feature as per Andi's comment.
> >   * Added warning debug log for MWAIT #VE exception.
> > 
> >   arch/x86/kernel/tdx.c | 23 +++++++++++++++++++++++
> >   1 file changed, 23 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> > index e936b2f88bf6..fb7d22b846fc 100644
> > --- a/arch/x86/kernel/tdx.c
> > +++ b/arch/x86/kernel/tdx.c
> > @@ -308,6 +308,9 @@ void __init tdx_early_init(void)
> >   	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
> > +	/* MWAIT is not supported in TDX platform, so suppress it */
> > +	setup_clear_cpu_cap(X86_FEATURE_MWAIT);
> 
> In fact, MWAIT bit returned by CPUID instruction is zero for TD guest. This
> is enforced by SEAM module.

Good point.
> 
> Do we still need to safeguard it by setup_clear_cpu_cap() here?

I guess it doesn't hurt to do it explicitly.


-Andi