linux-kernel - Re: [RFC v1 03/26] x86/cpufeatures: Add is_tdx

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Date:   Thu, 1 Apr 2021 14:15:52 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC v1 03/26] x86/cpufeatures: Add is_tdx_guest() interface



On 4/1/21 2:08 PM, Dave Hansen wrote:
> On 2/5/21 3:38 PM, Kuppuswamy Sathyanarayanan wrote:
>> +bool is_tdx_guest(void)
>> +{
>> +	return static_cpu_has(X86_FEATURE_TDX_GUEST);
>> +}
> 
> Why do you need is_tdx_guest() as opposed to calling
> cpu_feature_enabled(X86_FEATURE_TDX_GUEST) everywhere?

is_tdx_guest() is also implemented/used in compressed
code (which uses native_cpuid calls). I don't think
we can use cpu_feature_enabled(X86_FEATURE_TDX_GUEST) in
compressed code right? Also is_tdx_guest() looks easy
to read and use.
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer