Re: [RFC PATCH 2/4] KVM: selftests: Align memory region addresses to 1M on s390x

David Hildenbrand
2019-05-16T11:30:16Z

On 16.05.19 13:12, Thomas Huth wrote:
> On s390x, there is a constraint that memory regions have to be aligned
> to 1M (or running the VM will fail). Introduce a new "alignment" variable
> in the vm_userspace_mem_region_add() function which now can be used for
> both, huge page and s390x alignment requirements.
>
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
> tools/testing/selftests/kvm/lib/kvm_util.c | 21 +++++++++++++++++-----
> 1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 8d63ccb93e10..64a0da6efe3d 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -559,6 +559,7 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
> unsigned long pmem_size = 0;
> struct userspace_mem_region *region;
> size_t huge_page_size = KVM_UTIL_PGS_PER_HUGEPG * vm->page_size;
> + size_t alignment;
>
> TEST_ASSERT((guest_paddr % vm->page_size) == 0, "Guest physical "
> "address not on a page boundary.\n"
> @@ -608,9 +609,20 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
> TEST_ASSERT(region != NULL, "Insufficient Memory");
> region->mmap_size = npages * vm->page_size;
>
> - /* Enough memory to align up to a huge page. */
> +#ifdef __s390x__
> + /* On s390x, the host address must be aligned to 1M (due to PGSTEs) */
> + alignment = 0x100000;

This corresponds to huge_page_size, maybe you can exploit this fact here.

Something like

alignment = 1;

/* On s390x, the host address must always be aligned to the THP size */
#ifndef __s390x__
if (src_type == VM_MEM_SRC_ANONYMOUS_THP)
#endif
alignment = huge_page_size;

Maybe in a nicer fashion. Not sure.

> +#else
> + alignment = 1;
> +#endif
> +
> if (src_type == VM_MEM_SRC_ANONYMOUS_THP)
> - region->mmap_size += huge_page_size;
> + alignment = huge_page_size;
> +
> + /* Add enough memory to align up if necessary */
> + if (alignment > 1)
> + region->mmap_size += alignment;
> +
> region->mmap_start = mmap(NULL, region->mmap_size,
> PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANONYMOUS
> @@ -620,9 +632,8 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
> "test_malloc failed, mmap_start: %p errno: %i",
> region->mmap_start, errno);
>
> - /* Align THP allocation up to start of a huge page. */
> - region->host_mem = align(region->mmap_start,
> - src_type == VM_MEM_SRC_ANONYMOUS_THP ? huge_page_size : 1);
> + /* Align host address */
> + region->host_mem = align(region->mmap_start, alignment);
>
> /* As needed perform madvise */
> if (src_type == VM_MEM_SRC_ANONYMOUS || src_type == VM_MEM_SRC_ANONYMOUS_THP) {
>

--

Thanks,

David / dhildenb