[RFC PATCH v1 30/37] KVM: selftests: Provide function to look up guest_memfd details from gpa

[Ackerley Tng <ackerleytng@google.com>]

Introduce a new helper, kvm_gpa_to_guest_memfd(), to find the
guest_memfd-related details of a memory region that contains a given guest
physical address (GPA).

The function returns the file descriptor for the memfd, the offset into
the file that corresponds to the GPA, and the number of bytes remaining
in the region from that GPA.

kvm_gpa_to_guest_memfd() was factored out from vm_guest_mem_fallocate();
refactor vm_guest_mem_fallocate() to use the new helper.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 .../testing/selftests/kvm/include/kvm_util.h  |  3 ++
 tools/testing/selftests/kvm/lib/kvm_util.c    | 34 ++++++++++++-------
 2 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index dd26a41106fae..e9c2696770cf0 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -404,6 +404,9 @@ static inline void vm_enable_cap(struct kvm_vm *vm, uint32_t cap, uint64_t arg0)
 	vm_ioctl(vm, KVM_ENABLE_CAP, &enable_cap);
 }
 
+int kvm_gpa_to_guest_memfd(struct kvm_vm *vm, vm_paddr_t gpa, off_t *fd_offset,
+			   uint64_t *nr_bytes);
+
 #define TEST_REQUIRE_SET_MEMORY_ATTRIBUTES2()				\
 	__TEST_REQUIRE(kvm_has_cap(KVM_CAP_MEMORY_ATTRIBUTES2),		\
 		       "KVM selftests now require KVM_SET_MEMORY_ATTRIBUTES2")
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index c9c59f3ecd14f..cb73566fdf153 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1244,27 +1244,19 @@ void vm_guest_mem_fallocate(struct kvm_vm *vm, uint64_t base, uint64_t size,
 			    bool punch_hole)
 {
 	const int mode = FALLOC_FL_KEEP_SIZE | (punch_hole ? FALLOC_FL_PUNCH_HOLE : 0);
-	struct userspace_mem_region *region;
 	uint64_t end = base + size;
 	uint64_t gpa, len;
 	off_t fd_offset;
-	int ret;
+	int fd, ret;
 
 	for (gpa = base; gpa < end; gpa += len) {
-		uint64_t offset;
+		fd = kvm_gpa_to_guest_memfd(vm, gpa, &fd_offset, &len);
+		len = min(end - gpa, len);
 
-		region = userspace_mem_region_find(vm, gpa, gpa);
-		TEST_ASSERT(region && region->region.flags & KVM_MEM_GUEST_MEMFD,
-			    "Private memory region not found for GPA 0x%lx", gpa);
-
-		offset = gpa - region->region.guest_phys_addr;
-		fd_offset = region->region.guest_memfd_offset + offset;
-		len = min_t(uint64_t, end - gpa, region->region.memory_size - offset);
-
-		ret = fallocate(region->region.guest_memfd, mode, fd_offset, len);
+		ret = fallocate(fd, mode, fd_offset, len);
 		TEST_ASSERT(!ret, "fallocate() failed to %s at %lx (len = %lu), fd = %d, mode = %x, offset = %lx",
 			    punch_hole ? "punch hole" : "allocate", gpa, len,
-			    region->region.guest_memfd, mode, fd_offset);
+			    fd, mode, fd_offset);
 	}
 }
 
@@ -1673,6 +1665,22 @@ void *addr_gpa2alias(struct kvm_vm *vm, vm_paddr_t gpa)
 	return (void *) ((uintptr_t) region->host_alias + offset);
 }
 
+int kvm_gpa_to_guest_memfd(struct kvm_vm *vm, vm_paddr_t gpa, off_t *fd_offset,
+			   uint64_t *nr_bytes)
+{
+	struct userspace_mem_region *region;
+	vm_paddr_t gpa_offset;
+
+	region = userspace_mem_region_find(vm, gpa, gpa);
+	TEST_ASSERT(region && region->region.flags & KVM_MEM_GUEST_MEMFD,
+		    "guest_memfd memory region not found for GPA 0x%lx", gpa);
+
+	gpa_offset = gpa - region->region.guest_phys_addr;
+	*fd_offset = region->region.guest_memfd_offset + gpa_offset;
+	*nr_bytes = region->region.memory_size - gpa_offset;
+	return region->fd;
+}
+
 /* Create an interrupt controller chip for the specified VM. */
 void vm_create_irqchip(struct kvm_vm *vm)
 {
-- 
2.51.0.858.gf9c4a03a3a-goog