Messages in this thread | | | Subject | Re: [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature | From | "Kuppuswamy, Sathyanarayanan" <> | Date | Wed, 6 Oct 2021 08:43:48 -0700 |
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On 10/6/21 8:26 AM, Borislav Petkov wrote: > 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.
Yes. But, Joerg Roedel in his review recommended using variable similar to sme_me_mask to avoid function call in Intel platform in cc_platform_has().
" 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? "
That's why I have introduced is_tdx_guest global variable in this version.
> > /* > * 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"); > } >
-- Sathyanarayanan Kuppuswamy Linux Kernel Developer
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