[PATCH v10 14/16] KVM: arm64: Enable mapping guest_memfd in arm64

[Fuad Tabba <tabba@google.com>]

Enable mapping guest_memfd backed memory at the host in arm64. For now,
it applies to all arm64 VM types in arm64 that use guest_memfd. In the
future, new VM types can restrict this via
kvm_arch_gmem_supports_shared_mem().

Signed-off-by: Fuad Tabba <tabba@google.com>
---
 arch/arm64/include/asm/kvm_host.h | 5 +++++
 arch/arm64/kvm/Kconfig            | 1 +
 arch/arm64/kvm/mmu.c              | 7 +++++++
 3 files changed, 13 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 08ba91e6fb03..8add94929711 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -1593,4 +1593,9 @@ static inline bool kvm_arch_has_irq_bypass(void)
 	return true;
 }
 
+#ifdef CONFIG_KVM_GMEM
+#define kvm_arch_supports_gmem(kvm) true
+#define kvm_arch_supports_gmem_shared_mem(kvm) IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM)
+#endif
+
 #endif /* __ARM64_KVM_HOST_H__ */
diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index 096e45acadb2..8c1e1964b46a 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -38,6 +38,7 @@ menuconfig KVM
 	select HAVE_KVM_VCPU_RUN_PID_CHANGE
 	select SCHED_INFO
 	select GUEST_PERF_EVENTS if PERF_EVENTS
+	select KVM_GMEM_SHARED_MEM
 	help
 	  Support hosting virtualized guest machines.
 
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 896c56683d88..03da08390bf0 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -2264,6 +2264,13 @@ 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 shared memory, since
+	 * there aren't any CoCo VMs that support only private memory on arm64.
+	 */
+	if (kvm_slot_has_gmem(new) && !kvm_gmem_memslot_supports_shared(new))
+		return -EINVAL;
+
 	hva = new->userspace_addr;
 	reg_end = hva + (new->npages << PAGE_SHIFT);
 
-- 
2.49.0.1164.gab81da1b16-goog