linux-kernel - Re: [PATCH v8 04/11] x86/tdx: Add Intel ARCH support to cc_platform

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Date:   Wed, 6 Oct 2021 20:02:02 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...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>,
        Dave Hansen <dave.hansen@...el.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>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 04/11] x86/tdx: Add Intel ARCH support to
 cc_platform_has()

On Tue, Oct 05, 2021 at 02:16:11PM -0700, Josh Poimboeuf wrote:
> I assume this needs a rebase on -tip since cc_platform.c already has an
> empty version of this function (and it's static so it doesn't need to be
> declared in a header).

Yes:

arch/x86/kernel/cc_platform.c:16:28: error: static declaration of ‘intel_cc_platform_has’ follows non-static declaration
   16 | static bool __maybe_unused intel_cc_platform_has(enum cc_attr attr)
      |                            ^~~~~~~~~~~~~~~~~~~~~
In file included from ./include/linux/mem_encrypt.h:17,
                 from arch/x86/kernel/cc_platform.c:12:
./arch/x86/include/asm/mem_encrypt.h:105:6: note: previous declaration of ‘intel_cc_platform_has’ was here
  105 | bool intel_cc_platform_has(enum cc_attr attr);
      |      ^~~~~~~~~~~~~~~~~~~~~
make[2]: *** [scripts/Makefile.build:277: arch/x86/kernel/cc_platform.o] Error 1
make[1]: *** [scripts/Makefile.build:540: arch/x86/kernel] Error 2
make: *** [Makefile:1868: arch/x86] Error 2
make: *** Waiting for unfinished jobs....

I had already started that function there - please add all TDX logic in
cc_platform.c.

When you do your next set, you can use tip/master as a base. This should
be used for all x86 patchsets anyway.

> > +	/**
> > +	 * @CC_ATTR_GUEST_TDX: Trusted Domain Extension Support
> > +	 *
> > +	 * The platform/OS is running as a TDX guest/virtual machine.
> > +	 *
> > +	 * Examples include Intel TDX.
> > +	 */
> > +	CC_ATTR_GUEST_TDX,
> 
> Examples of TDX include TDX? :-)

Yeah, so whether we should be naming the actual conf. computing
implementation came up during the cc_platform_has() review and looking
forward in this patchset:

+       if (cc_platform_has(CC_ATTR_GUEST_TDX))
+               return tdx_kvm_hypercall(nr, 0, 0, 0, 0);

you really need to test for TDX because you're doing a TDX-specific
hypercall.

Which brings me back to the fastpath use of is_idx_guest(): this
looks to me like a fastpath use - dunno how often one needs to do TDX
hypercalls so I can imagine that for this, the is_tdx_guest() check
should use a static branch.

But only with numbers to show the need for it.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette