On 23/10/2025 6:16 pm, Sean Christopherson wrote:
On Mon, Oct 13, 2025, Jack Thomson wrote:
From: Jack Thomson jackabt@amazon.com
When creating a VM using mmap with huge pages, and the memory amount does not align with the underlying page size. The stored mmap_size value does not account for the fact that mmap will automatically align the length to a multiple of the underlying page size. During the teardown of the test, munmap is used. However, munmap requires the length to be a multiple of the underlying page size.
What happens when selftests use the wrong map_size? E.g. is munmap() silently failing? If so, then I should probably take this particular patch through kvm-x86/gmem, otherwise it means we'll start getting asserts due to:
3223560c93eb ("KVM: selftests: Define wrappers for common syscalls to assert success")
If munmap() isn't failing, then that begs the question of what this patch is actually doing :-)
Hi Sean, sorry I completely missed your reply.
Yeah currently with a misaligned map_size it causes munmap() to fail, I noticed when tested with different backings.
Update the vm_mem_add method to ensure the mmap_size is aligned to the underlying page size.
Signed-off-by: Jack Thomson jackabt@amazon.com
tools/testing/selftests/kvm/lib/kvm_util.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c index c3f5142b0a54..b106fbed999c 100644 --- a/tools/testing/selftests/kvm/lib/kvm_util.c +++ b/tools/testing/selftests/kvm/lib/kvm_util.c @@ -1051,7 +1051,6 @@ 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;
#ifdef __s390x__ /* On s390x, the host address must be aligned to 1M (due to PGSTEs) */ @@ -1060,6 +1059,11 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type, alignment = 1; #endif
- alignment = max(backing_src_pagesz, alignment);
- region->mmap_size = align_up(mem_size, alignment);
- TEST_ASSERT_EQ(guest_paddr, align_up(guest_paddr, backing_src_pagesz));
- /*
- 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
@@ -1067,12 +1071,6 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type, * page size. */ if (src_type == VM_MEM_SRC_ANONYMOUS_THP)
alignment = max(backing_src_pagesz, alignment);- TEST_ASSERT_EQ(guest_paddr, align_up(guest_paddr, backing_src_pagesz));
- /* Add enough memory to align up if necessary */
- if (alignment > 1) region->mmap_size += alignment;
region->fd = -1; -- 2.43.0