[RFC PATCH v2 15/37] KVM: selftests: Add support for mmap() on guest_memfd in core library

[Ackerley Tng <ackerleytng@google.com>]

From: Sean Christopherson <seanjc@google.com>

Accept gmem_flags in vm_mem_add() to be able to create a guest_memfd within
vm_mem_add().

When vm_mem_add() is used to set up a guest_memfd for a memslot, set up the
provided (or created) gmem_fd as the fd for the user memory region. This
makes it available to be mmap()-ed from just like fds from other memory
sources. mmap() from guest_memfd using the provided gmem_flags and
gmem_offset.

Add a kvm_slot_to_fd() helper to provide convenient access to the file
descriptor of a memslot.

Update existing callers of vm_mem_add() to pass 0 for gmem_flags to
preserve existing behavior.

Signed-off-by: Sean Christopherson <seanjc@google.com>
[For guest_memfds, mmap() using gmem_offset instead of 0 all the time.]
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 .../testing/selftests/kvm/include/kvm_util.h  |  7 ++++++-
 tools/testing/selftests/kvm/lib/kvm_util.c    | 19 +++++++++++--------
 .../kvm/x86/private_mem_conversions_test.c    |  2 +-
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index 81f4355ff28a..a64aae271a6a 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -678,7 +678,7 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
 				 uint32_t flags);
 void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 		uint64_t gpa, uint32_t slot, uint64_t npages, uint32_t flags,
-		int guest_memfd_fd, uint64_t guest_memfd_offset);
+		int gmem_fd, uint64_t gmem_offset, uint64_t gmem_flags);
 
 #ifndef vm_arch_has_protected_memory
 static inline bool vm_arch_has_protected_memory(struct kvm_vm *vm)
@@ -712,6 +712,11 @@ void *addr_gva2hva(struct kvm_vm *vm, vm_vaddr_t gva);
 vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva);
 void *addr_gpa2alias(struct kvm_vm *vm, vm_paddr_t gpa);
 
+static inline int kvm_slot_to_fd(struct kvm_vm *vm, uint32_t slot)
+{
+	return memslot2region(vm, slot)->fd;
+}
+
 #ifndef vcpu_arch_put_guest
 #define vcpu_arch_put_guest(mem, val) do { (mem) = (val); } while (0)
 #endif
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 6daeb4f945a0..ce2b0273b26c 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -946,12 +946,13 @@ void vm_set_user_memory_region2(struct kvm_vm *vm, uint32_t slot, 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 gpa, uint32_t slot, uint64_t npages, uint32_t flags,
-		int gmem_fd, uint64_t gmem_offset)
+		int gmem_fd, uint64_t gmem_offset, uint64_t gmem_flags)
 {
 	int ret;
 	struct userspace_mem_region *region;
 	size_t backing_src_pagesz = get_backing_src_pagesz(src_type);
 	size_t mem_size = npages * vm->page_size;
+	off_t mmap_offset = 0;
 	size_t alignment;
 
 	TEST_REQUIRE_SET_USER_MEMORY_REGION2();
@@ -1030,8 +1031,6 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 
 	if (flags & KVM_MEM_GUEST_MEMFD) {
 		if (gmem_fd < 0) {
-			uint32_t gmem_flags = 0;
-
 			TEST_ASSERT(!gmem_offset,
 				    "Offset must be zero when creating new guest_memfd");
 			gmem_fd = vm_create_guest_memfd(vm, mem_size, gmem_flags);
@@ -1052,13 +1051,17 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 	}
 
 	region->fd = -1;
-	if (backing_src_is_shared(src_type))
+	if (flags & KVM_MEM_GUEST_MEMFD && gmem_flags & GUEST_MEMFD_FLAG_MMAP) {
+		region->fd = kvm_dup(gmem_fd);
+		mmap_offset = gmem_offset;
+	} else if (backing_src_is_shared(src_type)) {
 		region->fd = kvm_memfd_alloc(region->mmap_size,
 					     src_type == VM_MEM_SRC_SHARED_HUGETLB);
+	}
 
-	region->mmap_start = kvm_mmap(region->mmap_size, PROT_READ | PROT_WRITE,
-				      vm_mem_backing_src_alias(src_type)->flag,
-				      region->fd);
+	region->mmap_start = __kvm_mmap(region->mmap_size, PROT_READ | PROT_WRITE,
+					vm_mem_backing_src_alias(src_type)->flag,
+					region->fd, mmap_offset);
 
 	TEST_ASSERT(!is_backing_src_hugetlb(src_type) ||
 		    region->mmap_start == align_ptr_up(region->mmap_start, backing_src_pagesz),
@@ -1119,7 +1122,7 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
 				 uint64_t gpa, uint32_t slot, uint64_t npages,
 				 uint32_t flags)
 {
-	vm_mem_add(vm, src_type, gpa, slot, npages, flags, -1, 0);
+	vm_mem_add(vm, src_type, gpa, slot, npages, flags, -1, 0, 0);
 }
 
 /*
diff --git a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
index 1969f4ab9b28..41f6b38f0407 100644
--- a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
+++ b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
@@ -399,7 +399,7 @@ static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t
 	for (i = 0; i < nr_memslots; i++)
 		vm_mem_add(vm, src_type, BASE_DATA_GPA + slot_size * i,
 			   BASE_DATA_SLOT + i, slot_size / vm->page_size,
-			   KVM_MEM_GUEST_MEMFD, memfd, slot_size * i);
+			   KVM_MEM_GUEST_MEMFD, memfd, slot_size * i, 0);
 
 	for (i = 0; i < nr_vcpus; i++) {
 		uint64_t gpa =  BASE_DATA_GPA + i * per_cpu_size;
-- 
2.53.0.rc1.225.gd81095ad13-goog