* Jeff Xu <jeffxu@xxxxxxxxxxxx> [230613 17:29]: > Hello Peter, > > Thanks for responding. > > On Tue, Jun 13, 2023 at 1:16 PM Peter Xu <peterx@xxxxxxxxxx> wrote: > > > > Hi, Jeff, > > > > On Tue, Jun 13, 2023 at 08:26:26AM -0700, Jeff Xu wrote: > > > + more ppl to the list. > > > > > > On Mon, Jun 12, 2023 at 6:04 PM Jeff Xu <jeffxu@xxxxxxxxxxxx> wrote: > > > > > > > > Hello, > > > > > > > > There seems to be inconsistency in different VMA fixup > > > > implementations, for example: > > > > mlock_fixup will skip VMA that is hugettlb, etc, but those checks do > > > > not exist in mprotect_fixup and madvise_update_vma. Wouldn't this be a > > > > problem? the merge/split skipped by mlock_fixup, might get acted on in > > > > the madvice/mprotect case. > > > > > > > > mlock_fixup currently check for > > > > if (newflags == oldflags || newflags == oldflags, then we don't need to do anything here, it's already at the desired mlock. mprotect does this, madvise does this.. probably.. it's ugly. > > > > (oldflags & VM_SPECIAL) || It's special, merging will fail always. I don't know about splitting, but I guess we don't want to alter the mlock state on special mappings. > > > > is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) || > > > > vma_is_dax(vma) || vma_is_secretmem(vma)) > > > > The special handling you mentioned in mlock_fixup mostly makes sense to me. > > > > E.g., I think we can just ignore mlock a hugetlb page if it won't be > > swapped anyway. > > > > Do you encounter any issue with above? > > > > > > Should there be a common function to handle VMA merge/split ? > > > > IMHO vma_merge() and split_vma() are the "common functions". Copy Lorenzo > > as I think he has plan to look into the interface to make it even easier to > > use. > > > The mprotect_fixup doesn't have the same check as mlock_fixup. When > userspace calls mlock(), two VMAs might not merge or split because of > vma_is_secretmem check, However, when user space calls mprotect() with > the same address range, it will merge/split. If mlock() is doing the > right thing to merge/split the VMAs, then mprotect() is not ? It looks like secretmem is mlock'ed to begin with so they don't want it to be touched. So, I think they will be treated differently and I think it is correct. Although, it would have been nice to have the comment above the function kept up to date on why certain VMAs are filtered out. > > Also skipping merge of VMA might be OK, but skipping split doesn't, > wouldn't that cause inconsistent between vma->vm_flags and what is > provisioned in the page ? I don't quite follow what you mean. It seems like the mlock_fixup() is skipped when we don't want the flag to be altered on a particular VMA. Where do they get out of sync?
