[PATCH v3 09/19] accel/kvm: Handle guest_memfd flags internally when creating instances

[Michael Roth <michael.roth@amd.com>]

Current hostmem code (which is callable even outside of KVM) specifies
guest_memfd flags directly, which requires pulling in kernel headers.
Additionally, it will eventually require additional knowledge that is
more suitable for KVM-aware code (e.g. whether or not to default to
private memory for confidential VMs).

Instead, push the determination for what flags are needed down into the
KVM/guest_memfd code so they can be handled internally based on VM
type/configuration and avoid further potential leakage of KVM-specific
code to general code.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 accel/kvm/kvm-all.c      | 26 ++++++++++++++++++++++++--
 accel/stubs/kvm-stub.c   |  2 +-
 backends/hostmem-memfd.c |  5 +----
 include/system/kvm.h     |  2 +-
 4 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 862539aed4..8cd1671ad5 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -4857,7 +4857,8 @@ 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)
+static int kvm_create_guest_memfd_flags(uint64_t size, uint64_t flags,
+                                        Error **errp)
 {
     int fd;
     struct kvm_create_guest_memfd guest_memfd = {
@@ -4897,6 +4898,27 @@ int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
     return fd;
 }
 
+int kvm_create_guest_memfd(uint64_t size, Error **errp)
+{
+    /*
+     * There isn't currently any use for non-mmap()'able gmem instances
+     * outside of kvm_create_guest_memfd_private(), so hardcode it here
+     * for general use.
+     *
+     * Additionally, *_INIT_SHARED is needed for non-confidential VMs, and
+     * confidential VMs will default to this as well to allow similar flows
+     * for initializing the VM's initial memory contents as with normal
+     * guests. In the future, the initial state may become a global policy
+     * decision based on the confidential VM configuration, in which case
+     * this would likely be the right place to decide whether or not to set
+     * the flag since it would likely be a globally-configured option.
+     */
+    return kvm_create_guest_memfd_flags(size,
+                                        GUEST_MEMFD_FLAG_MMAP |
+                                        GUEST_MEMFD_FLAG_INIT_SHARED,
+                                        errp);
+}
+
 int kvm_create_guest_memfd_private(uint64_t size, Error **errp)
 {
     if (!(kvm_supported_memory_attributes & KVM_MEMORY_ATTRIBUTE_PRIVATE)) {
@@ -4904,5 +4926,5 @@ int kvm_create_guest_memfd_private(uint64_t size, Error **errp)
         return -1;
     }
 
-    return kvm_create_guest_memfd(size, 0, errp);
+    return kvm_create_guest_memfd_flags(size, 0, errp);
 }
diff --git a/accel/stubs/kvm-stub.c b/accel/stubs/kvm-stub.c
index 9fe58efe91..26003b01a3 100644
--- a/accel/stubs/kvm-stub.c
+++ b/accel/stubs/kvm-stub.c
@@ -139,7 +139,7 @@ bool kvm_hwpoisoned_mem(void)
     return false;
 }
 
-int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
+int kvm_create_guest_memfd(uint64_t size, Error **errp)
 {
     error_setg(errp, "KVM is not enabled");
     return -ENOSYS;
diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
index c1ea6eefbd..d3b17232f0 100644
--- a/backends/hostmem-memfd.c
+++ b/backends/hostmem-memfd.c
@@ -70,10 +70,7 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
             return false;
         }
 
-        fd = kvm_create_guest_memfd(backend->size,
-                                    GUEST_MEMFD_FLAG_MMAP |
-                                    GUEST_MEMFD_FLAG_INIT_SHARED,
-                                    errp);
+        fd = kvm_create_guest_memfd(backend->size, errp);
     } else {
         fd = qemu_memfd_create(TYPE_MEMORY_BACKEND_MEMFD, backend->size,
                                m->hugetlb, m->hugetlbsize, m->seal ?
diff --git a/include/system/kvm.h b/include/system/kvm.h
index b1e43ddc93..2a1501bba6 100644
--- a/include/system/kvm.h
+++ b/include/system/kvm.h
@@ -547,7 +547,7 @@ void kvm_mark_guest_state_protected(void);
  */
 bool kvm_hwpoisoned_mem(void);
 
-int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp);
+int kvm_create_guest_memfd(uint64_t size, Error **errp);
 int kvm_create_guest_memfd_private(uint64_t size, Error **errp);
 
 int kvm_set_memory_attributes_private(hwaddr start, uint64_t size);
-- 
2.43.0