On Wed, Jul 20, 2022 at 01:58:06PM -0700, James Houghton wrote: > > > > > @@ -335,12 +337,16 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, > > > > > copied = 0; > > > > > page = NULL; > > > > > vma_hpagesize = vma_kernel_pagesize(dst_vma); > > > > > + if (use_hgm) > > > > > + vma_altpagesize = PAGE_SIZE; > > > > > > > > Do we need to check the "len" to know whether we should use sub-page > > > > mapping or original hpage size? E.g. any old UFFDIO_CONTINUE code will > > > > still want the old behavior I think. > > > > > > I think that's a fair point; however, if we enable HGM and the address > > > and len happen to be hstate-aligned > > > > The address can, but len (note! not "end" here) cannot? > > They both (dst_start and len) need to be hpage-aligned, otherwise we > won't be able to install hstate-sized PTEs. Like if we're installing > 4K at the beginning of a 1G hpage, we can't install a PUD, because we > only want to install that 4K. I'm still confused... Shouldn't one of the major goals of sub-page mapping is to grant user the capability to do UFFDIO_CONTINUE with len<hpagesize (so we install pages in sub-page level)? If so, why len needs to be always hpagesize aligned? -- Peter Xu
