Apply a1e2c031ec39 and e32683c6f7d2 to 5.15 and earlier

[Nathan Chancellor]

Hi Greg and Sasha,

Please consider applying the following mbox files to their respective
stable trees, which contains commit a1e2c031ec39 ("x86/mm: Simplify
RESERVE_BRK()") and commit e32683c6f7d2 ("x86/mm: Fix RESERVE_BRK() for
older binutils"). This resolves a link failure noticed in the Android
trees due to a new diagnostic in ld.lld:

https://github.com/llvm/llvm-project/commit/1981b1b6b92f7579a30c9ed32dbdf3bc749c1b40

  ld.lld: error: relocation refers to a symbol in a discarded section: __brk_reservation_fn_dmi_alloc__
  >>> defined in vmlinux.o
  >>> referenced by ld-temp.o
  >>>               vmlinux.o:(exit_amd_microcode.cfi_jt)

  ld.lld: error: relocation refers to a symbol in a discarded section: __brk_reservation_fn_early_pgt_alloc__
  >>> defined in vmlinux.o
  >>> referenced by ld-temp.o
  >>>               vmlinux.o:(exit_amd_microcode.cfi_jt)

While I think this may be related to Android's downstream use of LTO and
CFI, I see no reason that this could not happen without LTO due to
RESERVE_BRK() prior to those upstream commits residing in the
.discard.text section.

I confirmed they resolve the Android build problem and I did an
ARCH=x86_64 defconfig build and boot test in QEMU and an allmodconfig
build with GCC, which had no regressions.

Cheers,
Nathan

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