[PATCH v3 10/15] KVM: Add kvm_map_gfn_range

[Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>]

This new function establishes the mapping in KVM page tables for a
given gfn range. It can be used in the memory fallocate callback for
memfd based memory to establish the mapping for KVM secondary MMU when
the pages are allocated in the memory backend.

Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c   | 47 ++++++++++++++++++++++++++++++++++++++++
 include/linux/kvm_host.h |  2 ++
 virt/kvm/kvm_main.c      |  5 +++++
 3 files changed, 54 insertions(+)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 2da19356679d..a7006e1ac2d2 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1781,6 +1781,53 @@ static __always_inline bool kvm_handle_gfn_range(struct kvm *kvm,
 	return ret;
 }
 
+bool kvm_map_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	struct kvm_vcpu *vcpu;
+	kvm_pfn_t pfn;
+	gfn_t gfn;
+	int idx;
+	bool ret = true;
+
+	/* Need vcpu context for kvm_mmu_do_page_fault. */
+	vcpu = kvm_get_vcpu(kvm, 0);
+	if (mutex_lock_killable(&vcpu->mutex))
+		return false;
+
+	vcpu_load(vcpu);
+	idx = srcu_read_lock(&kvm->srcu);
+
+	kvm_mmu_reload(vcpu);
+
+	gfn = range->start;
+	while (gfn < range->end) {
+		if (signal_pending(current)) {
+			ret = false;
+			break;
+		}
+
+		if (need_resched())
+			cond_resched();
+
+		pfn = kvm_mmu_do_page_fault(vcpu, gfn << PAGE_SHIFT,
+					PFERR_WRITE_MASK | PFERR_USER_MASK,
+					false);
+		if (is_error_noslot_pfn(pfn) || kvm->vm_bugged) {
+			ret = false;
+			break;
+		}
+
+		gfn++;
+	}
+
+	srcu_read_unlock(&kvm->srcu, idx);
+	vcpu_put(vcpu);
+
+	mutex_unlock(&vcpu->mutex);
+
+	return ret;
+}
+
 bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	bool flush = false;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d9573305e273..9c02fb53b8ab 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -237,6 +237,8 @@ struct kvm_gfn_range {
 	pte_t pte;
 	bool may_block;
 };
+
+bool kvm_map_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
 bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
 bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d84cb867b686..b9855b2fdaae 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -456,6 +456,11 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_destroy);
 #if defined(CONFIG_MEMFD_OPS) ||\
 	(defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER))
 
+bool __weak kvm_map_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	return false;
+}
+
 typedef bool (*gfn_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);
 
 typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start,
-- 
2.17.1