linux-kernel - Re: [PATCH v6 11/11] x86/tdx: Handle CPUID via #VE

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Message-ID: <YTKzFJYy0CECENRX@google.com>
Date:   Fri, 3 Sep 2021 23:43:16 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Peter H Anvin <hpa@...or.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 11/11] x86/tdx: Handle CPUID via #VE

On Fri, Sep 03, 2021, Kuppuswamy, Sathyanarayanan wrote:
> 
> 
> On 9/3/21 11:35 AM, Dave Hansen wrote:
> > On 9/3/21 10:28 AM, Kuppuswamy Sathyanarayanan wrote:
> > > From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> > > 
> > > TDX has three classes of CPUID leaves: some CPUID leaves are always
> > > handled by the CPU, others are handled by the TDX module, and some
> > > others are handled by the VMM. Since the VMM cannot directly intercept
> > > the instruction these are reflected with a #VE exception to the guest,
> > > which then converts it into a hypercall to the VMM, or handled
> > > directly.
> > 
> > Does this patch do any of the "handled directly" leaves?  If not, why
> > mention it?
> 
> It was added to give more information about CPUID leaves handling. Since
> it has nothing to do with this patch, I can remove it.

What leaves are "always handled by the CPU"?  VTx doesn't allow disabling
CPUID exiting, let alone conditionally exiting on a specific CPUID leaf.  I don't
see anything in the TDX specs that suggests that's any different in SEAM non-root
mode.