[PATCH v5 3/7] KVM: arm64: Support dirty page tracking for PUD hugepages

In preparation for creating PUD hugepages at stage 2, add support for
write protecting PUD hugepages when they are encountered. Write
protecting guest tables is used to track dirty pages when migrating
VMs.

Also, provide trivial implementations of required kvm_s2pud_* helpers
to allow sharing of code with arm32.

Signed-off-by: Punit Agrawal <redacted>
Reviewed-by: Christoffer Dall <redacted>
Cc: Marc Zyngier <redacted>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <redacted>
---
  arch/arm/include/asm/kvm_mmu.h   | 16 ++++++++++++++++
  arch/arm64/include/asm/kvm_mmu.h | 10 ++++++++++
  virt/kvm/arm/mmu.c               | 11 +++++++----
  3 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index d095c2d0b284..c23722f75d5c 100644
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h

@@ -80,6 +80,22 @@ void kvm_clear_hyp_idmap(void);
  
  #define kvm_pmd_mkhuge(pmd)	pmd_mkhuge(pmd)
  
+/*
+ * The following kvm_*pud*() functionas are provided strictly to allow