x86/sev: Add full support for a segmented RMP table

A segmented RMP table allows for improved locality of reference between
the memory protected by the RMP and the RMP entries themselves.

Add support to detect and initialize a segmented RMP table with multiple
segments as configured by the system BIOS. While the RMPREAD instruction
will be used to read an RMP entry in a segmented RMP, initialization and
debugging capabilities will require the mapping of the segments.

The RMP_CFG MSR indicates if segmented RMP support is enabled and, if
enabled, the amount of memory that an RMP segment covers. When segmented
RMP support is enabled, the RMP_BASE MSR points to the start of the RMP
bookkeeping area, which is 16K in size. The RMP Segment Table (RST) is
located immediately after the bookkeeping area and is 4K in size. The RST
contains up to 512 8-byte entries that identify the location of the RMP
segment and amount of memory mapped by the segment (which must be less
than or equal to the configured segment size). The physical address that
is covered by a segment is based on the segment size and the index of the
segment in the RST. The RMP entry for a physical address is based on the
offset within the segment.

  For example, if the segment size is 64GB (0x1000000000 or 1 << 36), then
  physical address 0x9000800000 is RST entry 9 (0x9000800000 >> 36) and
  RST entry 9 covers physical memory 0x9000000000 to 0x9FFFFFFFFF.

  The RMP entry index within the RMP segment is the physical address
  AND-ed with the segment mask, 64GB - 1 (0xFFFFFFFFF), and then
  right-shifted 12 bits or PHYS_PFN(0x9000800000 & 0xFFFFFFFFF), which
  is 0x800.

CPUID 0x80000025_EBX[9:0] describes the number of RMP segments that can
be cached by the hardware. Additionally, if CPUID 0x80000025_EBX[10] is
set, then the number of actual RMP segments defined cannot exceed the
number of RMP segments that can be cached and can be used as a maximum
RST index.

  [ bp: Unify printk hex format specifiers. ]

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nikunj A Dadhania <nikunj@amd.com>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Link: https://lore.kernel.org/r/02afd0ffd097a19cb6e5fb1bb76eb110496c5b11.1734101742.git.thomas.lendacky@amd.com

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