linux-kernel - Re: [PATCH v5 04/12] x86/tdx: Add protected guest support for TDX guest

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Message-ID: <9c576f24-e6de-f816-623d-408a4a2ae747@intel.com>
Date:   Wed, 4 Aug 2021 15:03:30 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.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>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 04/12] x86/tdx: Add protected guest support for TDX
 guest

On 8/4/21 2:59 PM, Sean Christopherson wrote:
>> +#include <asm/processor.h>
>> +#include <asm/tdx.h>
>> +
>>  #ifndef __ASSEMBLY__
>>  
>>  static inline bool prot_guest_has(unsigned int attr)
>>  {
>>  	if (sme_me_mask)
>>  		return amd_prot_guest_has(attr);
>> +	else if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
> Why not "boot_cpu_has(X86_FEATURE_TDX_GUEST)"?

Even better: cpu_feature_enabled(X86_FEATURE_TDX_GUEST).  That gets you
both static patching *and* compile-time optimization if you hook
X86_FEATURE_TDX_GUEST into disabled-features.h.