KVM: selftests: x86: Add selftest for private memory conversions

Add a selftest to exercise implicit/explicit conversion functionality
within KVM and verify:

 - Shared memory is visible to host userspace
 - Private memory is not visible to host userspace
 - Host userspace and guest can communicate over shared memory
 - Data in shared backing is preserved across conversions (test's
   host userspace doesn't free the data)
 - Private memory is bound to the lifetime of the VM

TODO: rewrite this to allow backing a single region of guest memory with
mutliple memslots for _all_ backing types and shapes, i.e. make the code
for using a single backing fd across multiple memslots apply to regular
memory as well.

Signed-off-by: Vishal Annapurve <vannapurve@google.com>
Co-developed-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/Makefile

@@ -79,6 +79,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/monitor_mwait_test
 TEST_GEN_PROGS_x86_64 += x86_64/nested_exceptions_test
 TEST_GEN_PROGS_x86_64 += x86_64/platform_info_test
 TEST_GEN_PROGS_x86_64 += x86_64/pmu_event_filter_test
+TEST_GEN_PROGS_x86_64 += x86_64/private_mem_conversions_test
 TEST_GEN_PROGS_x86_64 += x86_64/set_boot_cpu_id
 TEST_GEN_PROGS_x86_64 += x86_64/set_sregs_test
 TEST_GEN_PROGS_x86_64 += x86_64/smaller_maxphyaddr_emulation_test

tools/testing/selftests/kvm/include/kvm_util_base.h

@@ -483,6 +483,9 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
 	enum vm_mem_backing_src_type src_type,
 	uint64_t guest_paddr, uint32_t slot, uint64_t npages,
 	uint32_t flags);
+void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
+		uint64_t guest_paddr, uint32_t slot, uint64_t npages,
+		uint32_t flags, int gmem_fd, uint64_t gmem_offset);
 
 void vm_mem_region_set_flags(struct kvm_vm *vm, uint32_t slot, uint32_t flags);
 void vm_mem_region_move(struct kvm_vm *vm, uint32_t slot, uint64_t new_gpa);

tools/testing/selftests/kvm/include/ucall_common.h

@@ -46,6 +46,18 @@ void ucall_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa);
 #define GUEST_SYNC_ARGS(stage, arg1, arg2, arg3, arg4)	\
 				ucall(UCALL_SYNC, 6, "hello", stage, arg1, arg2, arg3, arg4)
 #define GUEST_SYNC(stage)	ucall(UCALL_SYNC, 2, "hello", stage)
+
+#define GUEST_SYNC1(arg0) 	ucall(UCALL_SYNC, 1, arg0)
+#define GUEST_SYNC2(arg0, arg1) ucall(UCALL_SYNC, 2, arg0, arg1)
+#define GUEST_SYNC3(arg0, arg1, arg2) \
+				ucall(UCALL_SYNC, 3, arg0, arg1, arg2)
+#define GUEST_SYNC4(arg0, arg1, arg2, arg3) \
+				ucall(UCALL_SYNC, 4, arg0, arg1, arg2, arg3)
+#define GUEST_SYNC5(arg0, arg1, arg2, arg3, arg4) \
+				ucall(UCALL_SYNC, 5, arg0, arg1, arg2, arg3, arg4)
+#define GUEST_SYNC6(arg0, arg1, arg2, arg3, arg4, arg5) \
+				ucall(UCALL_SYNC, 6, arg0, arg1, arg2, arg3, arg4, arg5)
+
 #define GUEST_DONE()		ucall(UCALL_DONE, 0)
 
 enum guest_assert_builtin_args {

tools/testing/selftests/kvm/lib/kvm_util.c

@@ -849,32 +849,10 @@ void vm_set_user_memory_region(struct kvm_vm *vm, uint32_t slot, uint32_t flags,
 		    errno, strerror(errno));
 }
 
-/*
- * VM Userspace Memory Region Add
- *
- * Input Args:
- *   vm - Virtual Machine
- *   src_type - Storage source for this region.
- *              NULL to use anonymous memory.
- *   guest_paddr - Starting guest physical address
- *   slot - KVM region slot
- *   npages - Number of physical pages
- *   flags - KVM memory region flags (e.g. KVM_MEM_LOG_DIRTY_PAGES)
- *
- * Output Args: None
- *
- * Return: None
- *
- * Allocates a memory area of the number of pages specified by npages
- * and maps it to the VM specified by vm, at a starting physical address
- * given by guest_paddr.  The region is created with a KVM region slot
- * given by slot, which must be unique and < KVM_MEM_SLOTS_NUM.  The
- * region is created with the flags given by flags.
- */
-void vm_userspace_mem_region_add(struct kvm_vm *vm,
-	enum vm_mem_backing_src_type src_type,
-	uint64_t guest_paddr, uint32_t slot, uint64_t npages,
-	uint32_t flags)
+/* FIXME: This thing needs to be ripped apart and rewritten. */
+void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
+		uint64_t guest_paddr, uint32_t slot, uint64_t npages,
+		uint32_t flags, int gmem_fd, uint64_t gmem_offset)
 {
 	int ret;
 	struct userspace_mem_region *region;
@@ -989,8 +967,14 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
 	region->backing_src_type = src_type;
 
 	if (flags & KVM_MEM_PRIVATE) {
-		region->region.gmem_fd = vm_create_guest_memfd(vm, mem_size, 0);
-		region->region.gmem_offset = 0;
+		if (gmem_fd < 0) {
+			TEST_ASSERT(!gmem_offset,
+				    "Offset must be zero when creating new guest_memfd");
+			gmem_fd = vm_create_guest_memfd(vm, mem_size, 0);
+		}
+
+		region->region.gmem_fd = gmem_fd;
+		region->region.gmem_offset = gmem_offset;
 	}
 
 	region->unused_phy_pages = sparsebit_alloc();
@@ -1029,6 +1013,14 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
 	}
 }
 
+void vm_userspace_mem_region_add(struct kvm_vm *vm,
+				 enum vm_mem_backing_src_type src_type,
+				 uint64_t guest_paddr, uint32_t slot,
+				 uint64_t npages, uint32_t flags)
+{
+	vm_mem_add(vm, src_type, guest_paddr, slot, npages, flags, -1, 0);
+}
+
 /*
  * Memslot to region
  *