RAMBlock: Add support of KVM private guest memfd

Add KVM guest_memfd support to RAMBlock so both normal hva based memory
and kvm guest memfd based private memory can be associated in one RAMBlock.

Introduce new flag RAM_GUEST_MEMFD. When it's set, it calls KVM ioctl to
create private guest_memfd during RAMBlock setup.

Allocating a new RAM_GUEST_MEMFD flag to instruct the setup of guest memfd
is more flexible and extensible than simply relying on the VM type because
in the future we may have the case that not all the memory of a VM need
guest memfd. As a benefit, it also avoid getting MachineState in memory
subsystem.

Note, RAM_GUEST_MEMFD is supposed to be set for memory backends of
confidential guests, such as TDX VM. How and when to set it for memory
backends will be implemented in the following patches.

Introduce memory_region_has_guest_memfd() to query if the MemoryRegion has
KVM guest_memfd allocated.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-ID: <20240320083945.991426-7-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index db0b1a16ed..1b7bbd838c 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -92,6 +92,7 @@ static bool kvm_has_guest_debug;
 static int kvm_sstep_flags;
 static bool kvm_immediate_exit;
 static uint64_t kvm_supported_memory_attributes;
+static bool kvm_guest_memfd_supported;
 static hwaddr kvm_max_slot_size = ~0;
 
 static const KVMCapabilityInfo kvm_required_capabilites[] = {
@@ -2419,6 +2420,11 @@ static int kvm_init(MachineState *ms)
     }
 
     kvm_supported_memory_attributes = kvm_check_extension(s, KVM_CAP_MEMORY_ATTRIBUTES);
+    kvm_guest_memfd_supported =
+        kvm_check_extension(s, KVM_CAP_GUEST_MEMFD) &&
+        kvm_check_extension(s, KVM_CAP_USER_MEMORY2) &&
+        (kvm_supported_memory_attributes & KVM_MEMORY_ATTRIBUTE_PRIVATE);
+
     kvm_immediate_exit = kvm_check_extension(s, KVM_CAP_IMMEDIATE_EXIT);
     s->nr_slots = kvm_check_extension(s, KVM_CAP_NR_MEMSLOTS);
 
@@ -4138,3 +4144,25 @@ void kvm_mark_guest_state_protected(void)
 {
     kvm_state->guest_state_protected = true;
 }
+
+int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
+{
+    int fd;
+    struct kvm_create_guest_memfd guest_memfd = {
+        .size = size,
+        .flags = flags,
+    };
+
+    if (!kvm_guest_memfd_supported) {
+        error_setg(errp, "KVM does not support guest_memfd");
+        return -1;
+    }
+
+    fd = kvm_vm_ioctl(kvm_state, KVM_CREATE_GUEST_MEMFD, &guest_memfd);
+    if (fd < 0) {
+        error_setg_errno(errp, errno, "Error creating KVM guest_memfd");
+        return -1;
+    }
+
+    return fd;
+}