[PATCH v13 42/44] KVM: selftests: Set up page size and alignment independently for guest_memfd

[Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>]

From: Ackerley Tng <ackerleytng@google.com>

Currently, vm_mem_add derives the backing source page size, alignment
padding, and mmap size from the backing source type upfront before checking
if guest_memfd is being mmapped.

With shared memory also mmap()-ed from guest_memfd, the alignment of the
mmap-ed address needs to respect guest_memfd's backing page size.

Refactor the backing store setup to configure the backing source page
size, alignment, mmap flags, and mmap offset directly for guest_memfd
when it is mmapped, ignoring the backing source type.

Skip hugepage validation and anonymous memory madvise calls when mmapping
from guest_memfd, since those are not applicable when mmapping guest_memfd.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 tools/testing/selftests/kvm/lib/kvm_util.c | 74 ++++++++++++++++++------------
 1 file changed, 45 insertions(+), 29 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index cac5624e99774..3f559f207408f 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1034,11 +1034,12 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 {
 	int ret;
 	struct userspace_mem_region *region;
-	size_t backing_src_pagesz = get_backing_src_pagesz(src_type);
-	int mmap_flags = vm_mem_backing_src_alias(src_type)->flag;
 	size_t mem_size = npages * vm->page_size;
-	off_t mmap_offset = 0;
-	size_t alignment = 1;
+	size_t backing_src_pagesz;
+	off_t mmap_offset;
+	bool is_gmem_mmap;
+	size_t alignment;
+	int mmap_flags;
 
 	TEST_REQUIRE_SET_USER_MEMORY_REGION2();
 
@@ -1090,19 +1091,31 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 	/* Allocate and initialize new mem region structure. */
 	region = calloc(1, sizeof(*region));
 	TEST_ASSERT(region != NULL, "Insufficient Memory");
-	region->mmap_size = mem_size;
 
-	/*
-	 * When using THP mmap is not guaranteed to returned a hugepage aligned
-	 * address so we have to pad the mmap. Padding is not needed for HugeTLB
-	 * because mmap will always return an address aligned to the HugeTLB
-	 * page size.
-	 */
-	if (src_type == VM_MEM_SRC_ANONYMOUS_THP)
-		alignment = max(backing_src_pagesz, alignment);
+	is_gmem_mmap = (flags & KVM_MEM_GUEST_MEMFD) &&
+		       (gmem_flags & GUEST_MEMFD_FLAG_MMAP);
+
+	if (is_gmem_mmap) {
+		backing_src_pagesz = getpagesize();
+		alignment = 1;
+		mmap_flags = MAP_SHARED;
+		mmap_offset = gmem_offset;
+	} else {
+		backing_src_pagesz = get_backing_src_pagesz(src_type);
+		/*
+		 * When using THP mmap is not guaranteed to returned a hugepage aligned
+		 * address so we have to pad the mmap. Padding is not needed for HugeTLB
+		 * because mmap will always return an address aligned to the HugeTLB
+		 * page size.
+		 */
+		alignment = src_type == VM_MEM_SRC_ANONYMOUS_THP ? backing_src_pagesz : 1;
+		mmap_flags = vm_mem_backing_src_alias(src_type)->flag;
+		mmap_offset = 0;
+	}
 
 	TEST_ASSERT_EQ(gpa, align_up(gpa, backing_src_pagesz));
 
+	region->mmap_size = mem_size;
 	/* Add enough memory to align up if necessary */
 	if (alignment > 1)
 		region->mmap_size += alignment;
@@ -1129,10 +1142,8 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 	}
 
 	region->fd = -1;
-	if (flags & KVM_MEM_GUEST_MEMFD && gmem_flags & GUEST_MEMFD_FLAG_MMAP) {
+	if (is_gmem_mmap) {
 		region->fd = kvm_dup(gmem_fd);
-		mmap_flags = MAP_SHARED;
-		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);
@@ -1141,22 +1152,27 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 	region->mmap_start = __kvm_mmap(region->mmap_size, PROT_READ | PROT_WRITE,
 					mmap_flags, region->fd, mmap_offset);
 
-	TEST_ASSERT(!is_backing_src_hugetlb(src_type) ||
-		    region->mmap_start == align_ptr_up(region->mmap_start, backing_src_pagesz),
-		    "mmap_start %p is not aligned to HugeTLB page size 0x%lx",
-		    region->mmap_start, backing_src_pagesz);
-
 	/* Align host address */
 	region->host_mem = align_ptr_up(region->mmap_start, alignment);
 
-	/* As needed perform madvise */
-	if ((src_type == VM_MEM_SRC_ANONYMOUS ||
-	     src_type == VM_MEM_SRC_ANONYMOUS_THP) && thp_configured()) {
-		ret = madvise(region->host_mem, mem_size,
-			      src_type == VM_MEM_SRC_ANONYMOUS ? MADV_NOHUGEPAGE : MADV_HUGEPAGE);
-		TEST_ASSERT(ret == 0, "madvise failed, addr: %p length: 0x%lx src_type: %s",
-			    region->host_mem, mem_size,
-			    vm_mem_backing_src_alias(src_type)->name);
+	if (!is_gmem_mmap) {
+		TEST_ASSERT(!is_backing_src_hugetlb(src_type) ||
+			    region->mmap_start ==
+			    align_ptr_up(region->mmap_start, backing_src_pagesz),
+			    "mmap_start %p is not aligned to HugeTLB page size 0x%lx",
+			    region->mmap_start, backing_src_pagesz);
+
+		/* As needed perform madvise */
+		if ((src_type == VM_MEM_SRC_ANONYMOUS ||
+		     src_type == VM_MEM_SRC_ANONYMOUS_THP) && thp_configured()) {
+			int advice = src_type == VM_MEM_SRC_ANONYMOUS ?
+				     MADV_NOHUGEPAGE : MADV_HUGEPAGE;
+
+			ret = madvise(region->host_mem, mem_size, advice);
+			TEST_ASSERT(ret == 0, "madvise failed, addr: %p length: 0x%lx src_type: %s",
+				    region->host_mem, mem_size,
+				    vm_mem_backing_src_alias(src_type)->name);
+		}
 	}
 
 	region->backing_src_type = src_type;

-- 
2.55.0.1007.g17ff1f9808-goog