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    Subject[PATCHv2 01/29] x86/tdx: Detect running as a TDX guest in early boot
    Date
    From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

    cc_platform_has() API is used in the kernel to enable confidential
    computing features. Since TDX guest is a confidential computing
    platform, it also needs to use this API.

    In preparation of extending cc_platform_has() API to support TDX guest,
    use CPUID instruction to detect support for TDX guests in the early
    boot code (via tdx_early_init()). Since copy_bootdata() is the first
    user of cc_platform_has() API, detect the TDX guest status before it.

    Since cc_plaform_has() API will be used frequently across the boot
    code, instead of repeatedly detecting the TDX guest status using the
    CPUID instruction, detect once and cache the result. Add a function
    (is_tdx_guest()) to read the cached TDX guest status in CC APIs.

    Define a synthetic feature flag (X86_FEATURE_TDX_GUEST) and set this
    bit in a valid TDX guest platform. This feature bit will be used to
    do TDX-specific handling in some areas of the ARCH code where a
    function call to check for TDX guest status is not cost-effective
    (for example, TDX hypercall support).

    Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
    Reviewed-by: Andi Kleen <ak@linux.intel.com>
    Reviewed-by: Tony Luck <tony.luck@intel.com>
    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    arch/x86/Kconfig | 12 +++++++++
    arch/x86/include/asm/cpufeatures.h | 1 +
    arch/x86/include/asm/disabled-features.h | 8 +++++-
    arch/x86/include/asm/tdx.h | 23 ++++++++++++++++++
    arch/x86/kernel/Makefile | 1 +
    arch/x86/kernel/head64.c | 4 +++
    arch/x86/kernel/tdx.c | 31 ++++++++++++++++++++++++
    7 files changed, 79 insertions(+), 1 deletion(-)
    create mode 100644 arch/x86/include/asm/tdx.h
    create mode 100644 arch/x86/kernel/tdx.c

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index 6fddb63271d9..09e6744af3f8 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -880,6 +880,18 @@ config ACRN_GUEST
    IOT with small footprint and real-time features. More details can be
    found in https://projectacrn.org/.

    +config INTEL_TDX_GUEST
    + bool "Intel TDX (Trust Domain Extensions) - Guest Support"
    + depends on X86_64 && CPU_SUP_INTEL
    + depends on X86_X2APIC
    + help
    + Support running as a guest under Intel TDX. Without this support,
    + the guest kernel can not boot or run under TDX.
    + TDX includes memory encryption and integrity capabilities
    + which protect the confidentiality and integrity of guest
    + memory contents and CPU state. TDX guests are protected from
    + potential attacks from the VMM.
    +
    endif #HYPERVISOR_GUEST

    source "arch/x86/Kconfig.cpu"
    diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
    index 6db4e2932b3d..defed3bd543b 100644
    --- a/arch/x86/include/asm/cpufeatures.h
    +++ b/arch/x86/include/asm/cpufeatures.h
    @@ -238,6 +238,7 @@
    #define X86_FEATURE_VMW_VMMCALL ( 8*32+19) /* "" VMware prefers VMMCALL hypercall instruction */
    #define X86_FEATURE_PVUNLOCK ( 8*32+20) /* "" PV unlock function */
    #define X86_FEATURE_VCPUPREEMPT ( 8*32+21) /* "" PV vcpu_is_preempted function */
    +#define X86_FEATURE_TDX_GUEST ( 8*32+22) /* Intel Trust Domain Extensions Guest */

    /* Intel-defined CPU features, CPUID level 0x00000007:0 (EBX), word 9 */
    #define X86_FEATURE_FSGSBASE ( 9*32+ 0) /* RDFSBASE, WRFSBASE, RDGSBASE, WRGSBASE instructions*/
    diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
    index 8f28fafa98b3..f556086e6093 100644
    --- a/arch/x86/include/asm/disabled-features.h
    +++ b/arch/x86/include/asm/disabled-features.h
    @@ -65,6 +65,12 @@
    # define DISABLE_SGX (1 << (X86_FEATURE_SGX & 31))
    #endif

    +#ifdef CONFIG_INTEL_TDX_GUEST
    +# define DISABLE_TDX_GUEST 0
    +#else
    +# define DISABLE_TDX_GUEST (1 << (X86_FEATURE_TDX_GUEST & 31))
    +#endif
    +
    /*
    * Make sure to add features to the correct mask
    */
    @@ -76,7 +82,7 @@
    #define DISABLED_MASK5 0
    #define DISABLED_MASK6 0
    #define DISABLED_MASK7 (DISABLE_PTI)
    -#define DISABLED_MASK8 0
    +#define DISABLED_MASK8 (DISABLE_TDX_GUEST)
    #define DISABLED_MASK9 (DISABLE_SMAP|DISABLE_SGX)
    #define DISABLED_MASK10 0
    #define DISABLED_MASK11 0
    diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
    new file mode 100644
    index 000000000000..e375a950a033
    --- /dev/null
    +++ b/arch/x86/include/asm/tdx.h
    @@ -0,0 +1,23 @@
    +/* SPDX-License-Identifier: GPL-2.0 */
    +/* Copyright (C) 2021-2022 Intel Corporation */
    +#ifndef _ASM_X86_TDX_H
    +#define _ASM_X86_TDX_H
    +
    +#include <linux/init.h>
    +
    +#define TDX_CPUID_LEAF_ID 0x21
    +#define TDX_IDENT "IntelTDX "
    +
    +#ifdef CONFIG_INTEL_TDX_GUEST
    +
    +void __init tdx_early_init(void);
    +bool is_tdx_guest(void);
    +
    +#else
    +
    +static inline void tdx_early_init(void) { };
    +static inline bool is_tdx_guest(void) { return false; }
    +
    +#endif /* CONFIG_INTEL_TDX_GUEST */
    +
    +#endif /* _ASM_X86_TDX_H */
    diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
    index 6aef9ee28a39..211d9fcdd729 100644
    --- a/arch/x86/kernel/Makefile
    +++ b/arch/x86/kernel/Makefile
    @@ -130,6 +130,7 @@ obj-$(CONFIG_PARAVIRT_CLOCK) += pvclock.o
    obj-$(CONFIG_X86_PMEM_LEGACY_DEVICE) += pmem.o

    obj-$(CONFIG_JAILHOUSE_GUEST) += jailhouse.o
    +obj-$(CONFIG_INTEL_TDX_GUEST) += tdx.o

    obj-$(CONFIG_EISA) += eisa.o
    obj-$(CONFIG_PCSPKR_PLATFORM) += pcspeaker.o
    diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
    index de563db9cdcd..1cb6346ec3d1 100644
    --- a/arch/x86/kernel/head64.c
    +++ b/arch/x86/kernel/head64.c
    @@ -40,6 +40,7 @@
    #include <asm/extable.h>
    #include <asm/trapnr.h>
    #include <asm/sev.h>
    +#include <asm/tdx.h>

    /*
    * Manage page tables very early on.
    @@ -516,6 +517,9 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)

    copy_bootdata(__va(real_mode_data));

    + /* Needed before cc_platform_has() can be used for TDX */
    + tdx_early_init();
    +
    /*
    * Load microcode early on BSP.
    */
    diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
    new file mode 100644
    index 000000000000..1ef6979a6434
    --- /dev/null
    +++ b/arch/x86/kernel/tdx.c
    @@ -0,0 +1,31 @@
    +// SPDX-License-Identifier: GPL-2.0
    +/* Copyright (C) 2021-2022 Intel Corporation */
    +
    +#undef pr_fmt
    +#define pr_fmt(fmt) "tdx: " fmt
    +
    +#include <linux/cpufeature.h>
    +#include <asm/tdx.h>
    +
    +static bool tdx_guest_detected __ro_after_init;
    +
    +bool is_tdx_guest(void)
    +{
    + return tdx_guest_detected;
    +}
    +
    +void __init tdx_early_init(void)
    +{
    + u32 eax, sig[3];
    +
    + cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
    +
    + if (memcmp(TDX_IDENT, sig, 12))
    + return;
    +
    + tdx_guest_detected = true;
    +
    + setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
    +
    + pr_info("Guest detected\n");
    +}
    --
    2.34.1
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