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    Subject[PATCHv8 12/30] 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
    doesn't have a lot of call sites to IO instruction.

    To support port I/O in decompression code, TDX must be detected before
    the decompression code might do port I/O. Detect whether the kernel runs
    in a TDX guest.

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

    TDX is detected with CPUID. Make cpuid_count() accessible outside
    boot/cpuflags.c.

    TDX detection in the main kernel is very similar. Move common bits
    into <asm/shared/tdx.h>.

    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>
    Reviewed-by: Dave Hansen <dave.hansen@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 | 16 ++++++++++++++++
    arch/x86/boot/compressed/tdx.h | 13 +++++++++++++
    arch/x86/boot/cpuflags.c | 3 +--
    arch/x86/boot/cpuflags.h | 1 +
    arch/x86/include/asm/shared/tdx.h | 8 ++++++++
    arch/x86/include/asm/tdx.h | 4 +---
    9 files changed, 51 insertions(+), 5 deletions(-)
    create mode 100644 arch/x86/boot/compressed/tdx.c
    create mode 100644 arch/x86/boot/compressed/tdx.h
    create mode 100644 arch/x86/include/asm/shared/tdx.h

    diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
    index 6115274fe10f..732f6b21ecbd 100644
    --- a/arch/x86/boot/compressed/Makefile
    +++ b/arch/x86/boot/compressed/Makefile
    @@ -101,6 +101,7 @@ 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 1cdcaf34ee36..e8142e977ddb 100644
    --- a/arch/x86/boot/compressed/misc.c
    +++ b/arch/x86/boot/compressed/misc.c
    @@ -371,6 +371,14 @@ 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 TDX guest environment.
    + *
    + * It has to be done before console_init() in order to use
    + * paravirtualized port I/O operations 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..5f6d01a2f1f4
    --- /dev/null
    +++ b/arch/x86/boot/compressed/tdx.c
    @@ -0,0 +1,16 @@
    +// SPDX-License-Identifier: GPL-2.0
    +
    +#include "../cpuflags.h"
    +#include "../string.h"
    +
    +#include <asm/shared/tdx.h>
    +
    +void early_tdx_detect(void)
    +{
    + u32 eax, sig[3];
    +
    + cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
    +
    + if (memcmp(TDX_IDENT, sig, sizeof(sig)))
    + return;
    +}
    diff --git a/arch/x86/boot/compressed/tdx.h b/arch/x86/boot/compressed/tdx.h
    new file mode 100644
    index 000000000000..9055482cd35c
    --- /dev/null
    +++ b/arch/x86/boot/compressed/tdx.h
    @@ -0,0 +1,13 @@
    +/* SPDX-License-Identifier: GPL-2.0 */
    +#ifndef BOOT_COMPRESSED_TDX_H
    +#define BOOT_COMPRESSED_TDX_H
    +
    +#include <linux/types.h>
    +
    +#ifdef CONFIG_INTEL_TDX_GUEST
    +void early_tdx_detect(void);
    +#else
    +static inline void early_tdx_detect(void) { };
    +#endif
    +
    +#endif /* BOOT_COMPRESSED_TDX_H */
    diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
    index a0b75f73dc63..a83d67ec627d 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"
    diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
    index 2e20814d3ce3..475b8fde90f7 100644
    --- a/arch/x86/boot/cpuflags.h
    +++ b/arch/x86/boot/cpuflags.h
    @@ -17,5 +17,6 @@ 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);

    #endif
    diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
    new file mode 100644
    index 000000000000..8209ba9ffe1a
    --- /dev/null
    +++ b/arch/x86/include/asm/shared/tdx.h
    @@ -0,0 +1,8 @@
    +/* SPDX-License-Identifier: GPL-2.0 */
    +#ifndef _ASM_X86_SHARED_TDX_H
    +#define _ASM_X86_SHARED_TDX_H
    +
    +#define TDX_CPUID_LEAF_ID 0x21
    +#define TDX_IDENT "IntelTDX "
    +
    +#endif /* _ASM_X86_SHARED_TDX_H */
    diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
    index cbd61e142f4e..81a1ec14e476 100644
    --- a/arch/x86/include/asm/tdx.h
    +++ b/arch/x86/include/asm/tdx.h
    @@ -7,9 +7,7 @@
    #include <linux/init.h>
    #include <linux/bits.h>
    #include <asm/ptrace.h>
    -
    -#define TDX_CPUID_LEAF_ID 0x21
    -#define TDX_IDENT "IntelTDX "
    +#include <asm/shared/tdx.h>

    #define TDX_HYPERCALL_STANDARD 0

    --
    2.35.1
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