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    Subject[PATCH 09/26] x86/tdx: Detect TDX at early kernel decompression time
    Date
    From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

    The early decompression code does port I/O for its console output. But,
    handling the decompression-time port I/O demands a different approach
    from normal runtime because the IDT required to support #VE based port
    I/O emulation is not yet set up. Paravirtualizing I/O calls during
    the decompression step is acceptable because the decompression code size is
    small enough and hence patching it will not bloat the image size a lot.

    To support port I/O in decompression code, TDX must be detected before
    the decompression code might do port I/O. Add support to detect for
    TDX guest support before console_init() in the extract_kernel().
    Detecting it above the console_init() is early enough for patching
    port I/O.

    Add an early_is_tdx_guest() interface to get the cached TDX guest
    status in the decompression code.

    The actual port I/O paravirtualization will come later in the series.

    Reviewed-by: Tony Luck <tony.luck@intel.com>
    Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    arch/x86/boot/compressed/Makefile | 1 +
    arch/x86/boot/compressed/misc.c | 8 ++++++++
    arch/x86/boot/compressed/misc.h | 2 ++
    arch/x86/boot/compressed/tdx.c | 33 +++++++++++++++++++++++++++++++
    arch/x86/boot/compressed/tdx.h | 16 +++++++++++++++
    arch/x86/boot/cpuflags.c | 13 ++++++++++--
    arch/x86/boot/cpuflags.h | 2 ++
    7 files changed, 73 insertions(+), 2 deletions(-)
    create mode 100644 arch/x86/boot/compressed/tdx.c
    create mode 100644 arch/x86/boot/compressed/tdx.h

    diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
    index 431bf7f846c3..22a2a6cc2ab4 100644
    --- a/arch/x86/boot/compressed/Makefile
    +++ b/arch/x86/boot/compressed/Makefile
    @@ -98,6 +98,7 @@ ifdef CONFIG_X86_64
    endif

    vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
    +vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o

    vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
    efi-obj-$(CONFIG_EFI_STUB) = $(objtree)/drivers/firmware/efi/libstub/lib.a
    diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
    index a4339cb2d247..1b07755a5efd 100644
    --- a/arch/x86/boot/compressed/misc.c
    +++ b/arch/x86/boot/compressed/misc.c
    @@ -370,6 +370,14 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
    lines = boot_params->screen_info.orig_video_lines;
    cols = boot_params->screen_info.orig_video_cols;

    + /*
    + * Detect if we are running in TDX guest environment.
    + *
    + * It has to be done before console_init() to use paravirtualized
    + * port I/O oprations if needed.
    + */
    + early_tdx_detect();
    +
    console_init();

    /*
    diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
    index 16ed360b6692..0d8e275a9d96 100644
    --- a/arch/x86/boot/compressed/misc.h
    +++ b/arch/x86/boot/compressed/misc.h
    @@ -28,6 +28,8 @@
    #include <asm/bootparam.h>
    #include <asm/desc_defs.h>

    +#include "tdx.h"
    +
    #define BOOT_CTYPE_H
    #include <linux/acpi.h>

    diff --git a/arch/x86/boot/compressed/tdx.c b/arch/x86/boot/compressed/tdx.c
    new file mode 100644
    index 000000000000..2ee7d0bdf907
    --- /dev/null
    +++ b/arch/x86/boot/compressed/tdx.c
    @@ -0,0 +1,33 @@
    +// SPDX-License-Identifier: GPL-2.0
    +/*
    + * tdx.c - Early boot code for TDX
    + */
    +
    +#include "../cpuflags.h"
    +#include "../string.h"
    +
    +#define TDX_CPUID_LEAF_ID 0x21
    +#define TDX_IDENT "IntelTDX "
    +
    +static bool tdx_guest_detected;
    +
    +void early_tdx_detect(void)
    +{
    + u32 eax, sig[3];
    +
    + if (cpuid_max_leaf() < TDX_CPUID_LEAF_ID)
    + return;
    +
    + cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
    +
    + if (memcmp(TDX_IDENT, sig, 12))
    + return;
    +
    + /* Cache TDX guest feature status */
    + tdx_guest_detected = true;
    +}
    +
    +bool early_is_tdx_guest(void)
    +{
    + return tdx_guest_detected;
    +}
    diff --git a/arch/x86/boot/compressed/tdx.h b/arch/x86/boot/compressed/tdx.h
    new file mode 100644
    index 000000000000..18970c09512e
    --- /dev/null
    +++ b/arch/x86/boot/compressed/tdx.h
    @@ -0,0 +1,16 @@
    +/* SPDX-License-Identifier: GPL-2.0 */
    +/* Copyright (C) 2021 Intel Corporation */
    +#ifndef BOOT_COMPRESSED_TDX_H
    +#define BOOT_COMPRESSED_TDX_H
    +
    +#include <linux/types.h>
    +
    +#ifdef CONFIG_INTEL_TDX_GUEST
    +void early_tdx_detect(void);
    +bool early_is_tdx_guest(void);
    +#else
    +static inline void early_tdx_detect(void) { };
    +static inline bool early_is_tdx_guest(void) { return false; }
    +#endif
    +
    +#endif
    diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
    index a0b75f73dc63..7f97bf88c540 100644
    --- a/arch/x86/boot/cpuflags.c
    +++ b/arch/x86/boot/cpuflags.c
    @@ -71,8 +71,7 @@ int has_eflag(unsigned long mask)
    # define EBX_REG "=b"
    #endif

    -static inline void cpuid_count(u32 id, u32 count,
    - u32 *a, u32 *b, u32 *c, u32 *d)
    +void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
    {
    asm volatile(".ifnc %%ebx,%3 ; movl %%ebx,%3 ; .endif \n\t"
    "cpuid \n\t"
    @@ -82,6 +81,16 @@ static inline void cpuid_count(u32 id, u32 count,
    );
    }

    +/* Get maximum leaf value using CPUID(0) */
    +u32 cpuid_max_leaf(void)
    +{
    + u32 eax, ebx, ecx, edx;
    +
    + cpuid_count(0, 0, &eax, &ebx, &ecx, &edx);
    +
    + return eax;
    +}
    +
    #define cpuid(id, a, b, c, d) cpuid_count(id, 0, a, b, c, d)

    void get_cpuflags(void)
    diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
    index 2e20814d3ce3..dea67090a22f 100644
    --- a/arch/x86/boot/cpuflags.h
    +++ b/arch/x86/boot/cpuflags.h
    @@ -17,5 +17,7 @@ extern u32 cpu_vendor[3];

    int has_eflag(unsigned long mask);
    void get_cpuflags(void);
    +void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
    +u32 cpuid_max_leaf(void);

    #endif
    --
    2.32.0
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