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Date: Wed, 6 Oct 2021 17:26:33 +0200 From: Borislav Petkov <bp@...en8.de> To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com> Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>, David Hildenbrand <david@...hat.com>, Andrea Arcangeli <aarcange@...hat.com>, Josh Poimboeuf <jpoimboe@...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 Mon, Oct 04, 2021 at 07:51:57PM -0700, Kuppuswamy Sathyanarayanan wrote: > diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c > new file mode 100644 > index 000000000000..ad3ff5925153 > --- /dev/null > +++ b/arch/x86/kernel/tdx.c > @@ -0,0 +1,40 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* Copyright (C) 2020 Intel Corporation */ > + > +#undef pr_fmt > +#define pr_fmt(fmt) "tdx: " fmt > + > +#include <asm/tdx.h> > + > +/* > + * 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; > + > +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); > + > + pr_info("Guest initialized\n"); > +} > -- What I meant was this (untested of course). is_tdx_guest() is the accessor external code queries and you cache the detected value in tdx_guest so that the one after the first one is cheap. /* * 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. * * States whether the kernel is running as a TDX guest. */ static int tdx_guest __ro_after_init = -1; bool is_tdx_guest(void) { u32 eax, sig[3]; if (tdx_guest >= 0) return tdx_guest; if (cpuid_eax(0) < TDX_CPUID_LEAF_ID) { tdx_guest = 0; return false; } cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]); tdx_guest = !memcmp("IntelTDX ", sig, 12); return tdx_guest; } void __init tdx_early_init(void) { if (!is_tdx_guest()) return; setup_force_cpu_cap(X86_FEATURE_TDX_GUEST); pr_info("Guest initialized\n"); } -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
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