On Tue, Feb 11, 2020 at 5:53 AM Joerg Roedel [off-list ref] wrote:

From: Joerg Roedel <redacted>

The x86-64 ABI defines a red-zone on the stack:

  The 128-byte area beyond the location pointed to by %rsp is
  considered to be reserved and shall not be modified by signal or
  interrupt handlers. 10 Therefore, functions may use this area for
  temporary data that is not needed across function calls. In
  particular, leaf functions may use this area for their entire stack
  frame, rather than adjusting the stack pointer in the prologue and
  epilogue. This area is known as the red zone.

This is not compatible with exception handling, so disable it for the
pre-decompression boot code.

Acked-by: Andy Lutomirski <luto@kernel.org>

I admit that I thought we already supported exceptions this early.  At
least I seem to remember writing this code.  Maybe it never got
upstreamed?

--Andy