[PATCH 2/7] KVM: Add KVM_MAP_MEMORY vcpu ioctl to pre-populate guest memory

[Paolo Bonzini]

From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

Add a new ioctl KVM_MAP_MEMORY in the KVM common code. It iterates on the
memory range and calls the arch-specific function.  Add stub arch function
as a weak symbol.

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Message-ID: <819322b8f25971f2b9933bfa4506e618508ad782.1712785629.git.isaku.yamahata@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 include/linux/kvm_host.h |  5 ++++
 include/uapi/linux/kvm.h | 10 +++++++
 virt/kvm/Kconfig         |  3 ++
 virt/kvm/kvm_main.c      | 61 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 79 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 8dea11701ab2..2b0f0240a64c 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2478,4 +2478,9 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t gfn, void __user *src, long npages
 void kvm_arch_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end);
 #endif
 
+#ifdef CONFIG_KVM_GENERIC_MAP_MEMORY
+int kvm_arch_vcpu_map_memory(struct kvm_vcpu *vcpu,
+			     struct kvm_map_memory *mapping);
+#endif
+
 #endif
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 2190adbe3002..4d233f44c613 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -917,6 +917,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_MEMORY_ATTRIBUTES 233
 #define KVM_CAP_GUEST_MEMFD 234
 #define KVM_CAP_VM_TYPES 235
+#define KVM_CAP_MAP_MEMORY 236
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
@@ -1548,4 +1549,13 @@ struct kvm_create_guest_memfd {
 	__u64 reserved[6];
 };
 
+#define KVM_MAP_MEMORY	_IOWR(KVMIO, 0xd5, struct kvm_map_memory)
+
+struct kvm_map_memory {
+	__u64 base_address;
+	__u64 size;
+	__u64 flags;
+	__u64 padding[5];
+};
+
 #endif /* __LINUX_KVM_H */
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 754c6c923427..1b94126622e8 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -67,6 +67,9 @@ config HAVE_KVM_INVALID_WAKEUPS
 config KVM_GENERIC_DIRTYLOG_READ_PROTECT
        bool
 
+config KVM_GENERIC_MAP_MEMORY
+       bool
+
 config KVM_COMPAT
        def_bool y
        depends on KVM && COMPAT && !(S390 || ARM64 || RISCV)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 38b498669ef9..350ead98e9a6 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4379,6 +4379,47 @@ static int kvm_vcpu_ioctl_get_stats_fd(struct kvm_vcpu *vcpu)
 	return fd;
 }
 
+#ifdef CONFIG_KVM_GENERIC_MAP_MEMORY
+static int kvm_vcpu_map_memory(struct kvm_vcpu *vcpu,
+			       struct kvm_map_memory *mapping)
+{
+	int idx, r;
+	u64 full_size;
+
+	if (mapping->flags)
+		return -EINVAL;
+
+	if (!PAGE_ALIGNED(mapping->base_address) ||
+	    !PAGE_ALIGNED(mapping->size) ||
+	    mapping->base_address + mapping->size <= mapping->base_address)
+		return -EINVAL;
+
+	vcpu_load(vcpu);
+	idx = srcu_read_lock(&vcpu->kvm->srcu);
+
+	r = 0;
+	full_size = mapping->size;
+	while (mapping->size) {
+		if (signal_pending(current)) {
+			r = -EINTR;
+			break;
+		}
+
+		r = kvm_arch_vcpu_map_memory(vcpu, mapping);
+		if (r)
+			break;
+
+		cond_resched();
+	}
+
+	srcu_read_unlock(&vcpu->kvm->srcu, idx);
+	vcpu_put(vcpu);
+
+	/* Return success if at least one page was mapped successfully.  */
+	return full_size == mapping->size ? r : 0;
+}
+#endif
+
 static long kvm_vcpu_ioctl(struct file *filp,
 			   unsigned int ioctl, unsigned long arg)
 {
@@ -4580,6 +4621,20 @@ static long kvm_vcpu_ioctl(struct file *filp,
 		r = kvm_vcpu_ioctl_get_stats_fd(vcpu);
 		break;
 	}
+#ifdef CONFIG_KVM_GENERIC_MAP_MEMORY
+	case KVM_MAP_MEMORY: {
+		struct kvm_map_memory mapping;
+
+		r = -EFAULT;
+		if (copy_from_user(&mapping, argp, sizeof(mapping)))
+			break;
+		r = kvm_vcpu_map_memory(vcpu, &mapping);
+		/* Pass back leftover range. */
+		if (copy_to_user(argp, &mapping, sizeof(mapping)))
+			r = -EFAULT;
+		break;
+	}
+#endif
 	default:
 		r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
 	}
@@ -4863,6 +4918,12 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 #ifdef CONFIG_KVM_PRIVATE_MEM
 	case KVM_CAP_GUEST_MEMFD:
 		return !kvm || kvm_arch_has_private_mem(kvm);
+#endif
+#ifdef CONFIG_KVM_GENERIC_MAP_MEMORY
+	case KVM_CAP_MAP_MEMORY:
+		if (!kvm)
+			return 1;
+		/* Leave per-VM implementation to kvm_vm_ioctl_check_extension().  */
 #endif
 	default:
 		break;
-- 
2.43.0