x86/fred: Add FRED initialization functions

Add cpu_init_fred_exceptions() to:
- Set FRED entrypoints for events happening in ring 0 and 3.
- Specify the stack level for IRQs occurred ring 0.
- Specify dedicated event stacks for #DB/NMI/#MCE/#DF.
- Enable FRED and invalidtes IDT.
- Force 32-bit system calls to use "int $0x80" only.

Add fred_complete_exception_setup() to:
- Initialize system_vectors as done for IDT systems.
- Set unused sysvec_table entries to fred_handle_spurious_interrupt().

Co-developed-by: Xin Li <xin3.li@intel.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-35-xin3.li@intel.com

x86/entry: Add fred_entry_from_kvm() for VMX to handle IRQ/NMI

In IRQ/NMI induced VM exits, KVM VMX needs to execute the respective
handlers, which requires the software to create a FRED stack frame,
and use it to invoke the handlers. Add fred_irq_entry_from_kvm() for
this job.

Export fred_entry_from_kvm() because VMX can be compiled as a module.

Suggested-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-32-xin3.li@intel.com

x86/fred: FRED entry/exit and dispatch code

The code to actually handle kernel and event entry/exit using
FRED. It is split up into two files thus:

- entry_64_fred.S contains the actual entrypoints and exit code, and
saves and restores registers.

- entry_fred.c contains the two-level event dispatch code for FRED.
The first-level dispatch is on the event type, and the second-level
is on the event vector.

[ bp: Fold in an allmodconfig clang build fix:
https://lore.kernel.org/r/20240129064521.5168-1-xin3.li@intel.com
and a CONFIG_IA32_EMULATION=n build fix:
https://lore.kernel.org/r/20240127093728.1323-3-xin3.li@intel.com]

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Originally-by: Megha Dey <megha.dey@intel.com>
Co-developed-by: Xin Li <xin3.li@intel.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231209214214.2932-1-xin3.li@intel.com

x86/fred: Add a new header file for FRED definitions

Add a header file for FRED prototypes and definitions.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-16-xin3.li@intel.com