linux-kernel - Re: [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature

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Message-ID: <f15d1b41-e4fb-0203-88f7-dbac3f4e5307@linux.intel.com>
Date:   Tue, 5 Oct 2021 21:33:35 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        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 03/11] x86/cpufeatures: Add TDX Guest CPU feature



On 10/5/21 8:42 PM, Josh Poimboeuf wrote:
>> is_tdx_guest was mainly introduced to support cc_platform_has()
>> API in early boot calls (similar to sme_me_mask in AMD code).
>> Regarding FEATURE flag it will be useful for userspace tools to
>> check the TDX feature support.
> FEATURE flags can also be checked in the kernel, with boot_cpu_has().
> Or am I missing something?

Yes, previously we have been using x86_feature_enabled() check in
cc_platform_has() call. Now with the introduction of is_tdx_guest
global variable, we don't use it in kernel. But I still want to
keep the feature flag for user space use case.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer