To use HVO, make sure that the kernel is booted with pseudo-NMI
enabled by "irqchip.gicv3_pseudo_nmi=1", as well as
"hugetlb_free_vmemmap=on" unless HVO is enabled by default.

Note that HVO checks the pseudo-NMI capability and is disabled at
runtime if that turns out not supported. Successfully enabling HVO
should have the following:
  # dmesg | grep NMI
  GICv3: Pseudo-NMIs enabled using ...
  # sysctl vm.hugetlb_optimize_vmemmap
  vm.hugetlb_optimize_vmemmap = 1

For comparison purposes, the whole series was measured against this
patch only, to show the overhead from pausing remote CPUs:
  HugeTLB operations      This patch only   The whole series   Change
  Alloc 600 1GB                  0m3.526s           0m3.649s      +4%
  Free 600 1GB                   0m0.880s           0m0.917s      +4%
  Demote 600 1GB to 307200 2MB   0m1.575s           0m3.640s    +231%
  Free 307200 2MB                0m0.946s           0m2.921s    +309%

Signed-off-by: Yu Zhao <yuzhao@google.com>
---
 arch/arm64/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index fd9df6dcc593..e93745f819d9 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -109,6 +109,7 @@ config ARM64
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
+	select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
 	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WANTS_EXECMEM_LATE if EXECMEM
 	select ARCH_WANTS_NO_INSTR
-- 
2.47.0.277.g8800431eea-goog