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    SubjectRe: [PATCH 5/9] KVM: selftests: Align memory region addresses to 1M on s390x
    On Thu, May 23, 2019 at 06:43:05PM +0200, 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 08edb8436c47..656df9d5cd4d 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;
    > +#else
    > + alignment = 1;
    > +#endif
    > +
    > if (src_type == VM_MEM_SRC_ANONYMOUS_THP)
    > - region->mmap_size += huge_page_size;
    > + alignment = huge_page_size;

    I guess s390x won't ever support VM_MEM_SRC_ANONYMOUS_THP? If it does,
    then we need 'alignment = max(huge_page_size, alignment)'. Actually
    that might be a nice way to write this anyway for future-proofing.

    > +
    > + /* 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) {
    > --
    > 2.21.0
    >

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