On Thu, Feb 25, 2021, wangyanan (Y) wrote: > Hi Sean, > > On 2021/2/11 7:06, Sean Christopherson wrote: > > Align the HVA for HugeTLB memslots, not just THP memslots. Add an > > assert so any future backing types are forced to assess whether or not > > they need to be aligned. > > > > Cc: Ben Gardon <bgardon@xxxxxxxxxx> > > Cc: Yanan Wang <wangyanan55@xxxxxxxxxx> > > Cc: Andrew Jones <drjones@xxxxxxxxxx> > > Cc: Peter Xu <peterx@xxxxxxxxxx> > > Cc: Aaron Lewis <aaronlewis@xxxxxxxxxx> > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > > --- > > tools/testing/selftests/kvm/lib/kvm_util.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c > > index 584167c6dbc7..deaeb47b5a6d 100644 > > --- a/tools/testing/selftests/kvm/lib/kvm_util.c > > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c > > @@ -731,8 +731,11 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm, > > alignment = 1; > > #endif > > - if (src_type == VM_MEM_SRC_ANONYMOUS_THP) > > + if (src_type == VM_MEM_SRC_ANONYMOUS_THP || > > + src_type == VM_MEM_SRC_ANONYMOUS_HUGETLB) > Sorry for the late reply, I just returned from vacation. At least you had an excuse :-) > I am not sure HVA alignment is really necessary here for hugetlb pages. > Different from hugetlb pages, the THP pages are dynamically allocated by > later madvise(), so the value of HVA returned from mmap() is host page size > aligned but not THP page size aligned, so we indeed have to perform > alignment. But hugetlb pages are pre-allocated on systems. The following > test results also indicate that, with MAP_HUGETLB flag, the HVA returned from > mmap() is already aligned to the corresponding hugetlb page size. So maybe > HVAs of each hugetlb pages are aligned during allocation of them or in mmap()? Yep, I verified the generic and arch version of hugetlb_get_unmapped_area() that KVM supports all align the address. PARISC64 is the only one that looks suspect, but it doesn't support KVM. > If so, I think we better not do this again here, because the later > *region->mmap_size += alignment* will cause one more hugetlb page mapped but > will not be used. Agreed. I think I'll still add the assert, along with a comment calling out that HugetlB automatically handles alignment. Nice catch, thanks!
