On 23/10/2025 6:16 pm, Sean Christopherson wrote:
On Mon, Oct 13, 2025, Jack Thomson wrote:
From: Jack Thomson <[email protected]>
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 <[email protected]>
---
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
--
Thanks,
Jack
