Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 6 Oct 2021 07:25:59 -0700
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Juergen Gross <jgross@suse.com>, Deep Shah <sdeep@vmware.com>,
        VMware Inc <pv-drivers@vmware.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, Peter H Anvin <hpa@zytor.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature
Message-ID: <20211006142559.4s7exdrzhgpk6awl@treble>
References: <20211005025205.1784480-1-sathyanarayanan.kuppuswamy@linux.intel.com>
 <20211005025205.1784480-4-sathyanarayanan.kuppuswamy@linux.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20211005025205.1784480-4-sathyanarayanan.kuppuswamy@linux.intel.com>
Precedence: bulk

On Mon, Oct 04, 2021 at 07:51:57PM -0700, Kuppuswamy Sathyanarayanan wrote:
> +/*
> + * Allocate it in the data region to avoid zeroing it during
> + * BSS initialization. It is mainly used in cc_platform_has()
> + * call during early boot call.
> + */
> +u64 __section(".data") is_tdx_guest = 0;

Actually this should be __ro_after_init, since it never changes after
it's initialized.  As a bonus you won't have to worry about it getting
placed in BSS and the comment and initializer can go away.

> +
> +static void __init is_tdx_guest_init(void)
> +{
> +	u32 eax, sig[3];
> +
> +	if (cpuid_eax(0) < TDX_CPUID_LEAF_ID) {
> +		is_tdx_guest = 0;
> +		return;
> +	}
> +
> +	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
> +
> +	is_tdx_guest = !memcmp("IntelTDX    ", sig, 12);
> +}
> +
> +void __init tdx_early_init(void)
> +{
> +	is_tdx_guest_init();
> +
> +	if (!is_tdx_guest)
> +		return;
> +
> +	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);

setup_force_cpu_cap() sets a bit in 'cpu_caps_set' which is in BSS,
which gets cleared later right?  So this presumably doesn't fully work
as expected.  Maybe it can be set in init_intel(), based on
'is_tdx_guest'.

-- 
Josh