[PATCH v17 20/24] KVM: arm64: Enable support for guest_memfd backed memory

[Sean Christopherson]

From: Fuad Tabba <tabba@xxxxxxxxxx>

Now that the infrastructure is in place, enable guest_memfd for arm64.

* Select CONFIG_KVM_GUEST_MEMFD in KVM/arm64 Kconfig.

* Enforce KVM_MEMSLOT_GMEM_ONLY for guest_memfd on arm64: Ensure that
  guest_memfd-backed memory slots on arm64 are only supported if they
  are intended for shared memory use cases (i.e.,
  kvm_memslot_is_gmem_only() is true). This design reflects the current
  arm64 KVM ecosystem where guest_memfd is primarily being introduced
  for VMs that support shared memory.

Reviewed-by: James Houghton <jthoughton@xxxxxxxxxx>
Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/arm64/kvm/Kconfig | 1 +
 arch/arm64/kvm/mmu.c   | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index 713248f240e0..bff62e75d681 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -37,6 +37,7 @@ menuconfig KVM
 	select HAVE_KVM_VCPU_RUN_PID_CHANGE
 	select SCHED_INFO
 	select GUEST_PERF_EVENTS if PERF_EVENTS
+	select KVM_GUEST_MEMFD
 	help
 	  Support hosting virtualized guest machines.
 
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 8c82df80a835..85559b8a0845 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -2276,6 +2276,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	if ((new->base_gfn + new->npages) > (kvm_phys_size(&kvm->arch.mmu) >> PAGE_SHIFT))
 		return -EFAULT;
 
+	/*
+	 * Only support guest_memfd backed memslots with mappable memory, since
+	 * there aren't any CoCo VMs that support only private memory on arm64.
+	 */
+	if (kvm_slot_has_gmem(new) && !kvm_memslot_is_gmem_only(new))
+		return -EINVAL;
+
 	hva = new->userspace_addr;
 	reg_end = hva + (new->npages << PAGE_SHIFT);
 
-- 
2.50.1.552.g942d659e1b-goog