linux-kernel - Re: [PATCHv2 22/29] x86/tdx: Make pages shared in ioremap()

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Date:   Thu, 17 Feb 2022 16:24:05 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>, tglx@...utronix.de,
        mingo@...hat.com, luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 22/29] x86/tdx: Make pages shared in ioremap()

On Wed, Feb 16, 2022 at 06:37:03PM +0300, Kirill A. Shutemov wrote:
> 	bool cc_platform_has(enum cc_attr attr)
> 	{
> 		if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
> 			return intel_cc_platform_has(attr);
> 		else if (cc_mask)
> 			return amd_cc_platform_has(attr);

It is exactly stuff like that I'd like to avoid because that is
dependent on the order the test happens.

It would be a lot more robust if this did:

	switch (cc_vendor) {
	case INTEL:  return intel_cc_platform_has(attr);
	case AMD:    return amd_cc_platform_has(attr);
	case HYPERV: return hyperv_cc_platform_has(attr);
	default: return false;
	}

-- 
Regards/Gruss,
    Boris.

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