On 07/06/23 00:22, Matthew Wilcox wrote: > On Wed, Jul 05, 2023 at 04:08:08PM -0700, Mike Kravetz wrote: > > I was recently asked about the behavior of mprotect on a hugetlb > > mapping where addr or addr+len is not hugetlb page size aligned. As > > one might expect, EINVAL is returned in such cases. However, the man > > page makes no mention of alignment requirements for hugetlb mappings. > > > > I am happy to submit man page updates if people agree this is the correct > > behavior. We might even want to check alignment earlier in the code > > path as we fail when trying to split the vma today. > > > > An alternative behavior would be to operate on whole hugetlb pages within > > the range addr - addr+len. > > After a careful re-reading of the mprotect() man page, I suggest the > following behaviour ... > > addr must be a multiple of the hpage size. Otherwise -EINVAL. > len should be rounded up to hpage size. > > I wonder how likely this change would be to break userspace code. > Maybe some test cases. My concern is that this is the approach I took with huegtlb MADV_DONTNEED, and this caused problems discussed and eventually modified here: https://lore.kernel.org/linux-mm/20221021154546.57df96db@xxxxxxxxxxxxxxxxxxxx/ In the MADV_DONTNEED case we were throwing away data. With mprotect we are only modifying access to data. -- Mike Kravetz
