x86/mm: Handle global ASID context switch and TLB flush

x86/mm: Handle global ASID context switch and TLB flush

Do context switch and TLB flush support for processes that use a global
ASID and PCID across all CPUs.

At both context switch time and TLB flush time, it needs to be checked whether
a task is switching to a global ASID, and, if so, reload the TLB with the new
ASID as appropriate.

In both code paths, the TLB flush is avoided if a global ASID is used, because
the global ASIDs are always kept up to date across CPUs, even when the
process is not running on a CPU.

  [ bp:
   - Massage
   - :%s/\<static_cpu_has\>/cpu_feature_enabled/cgi
  ]

Signed-off-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250226030129.530345-9-riel@surriel.com