linux-kernel - Re: [PATCH v6 04/11] x86/tdx: Add protected guest support for TDX guest

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Message-ID: <20fc6806-0c46-15d6-930b-6b4e90dfee6d@linux.intel.com>
Date:   Tue, 28 Sep 2021 05:56:03 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     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>,
        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 v6 04/11] x86/tdx: Add protected guest support for TDX
 guest



On 9/28/21 4:46 AM, Joerg Roedel wrote:
> On Fri, Sep 03, 2021 at 10:28:05AM -0700, Kuppuswamy Sathyanarayanan wrote:
>>   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)
>> +		return intel_prot_guest_has(attr);
> 
> This causes a function call on every Intel machine this code runs. is
> there an easier to check whether TDX is enabled, like the sme_me_mask
> check on AMD?

This will only be called when CONFIG_ARCH_HAS_CC_PLATFORM is set by a platform.
So it won't be called for all platforms.

Also, intel_prot_guest_has() is a generic Intel platform branch call (so we can't
directly check for TDX here).

> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer