On Wed, May 17, 2023 at 02:54:39PM -0400, Peter Xu wrote: > On Wed, May 17, 2023 at 07:40:59PM +0100, Lorenzo Stoakes wrote: > > On Wed, May 17, 2023 at 02:37:41PM -0400, Peter Xu wrote: > > > On Wed, May 17, 2023 at 06:20:55PM +0100, Lorenzo Stoakes wrote: > > > > On Wed, May 17, 2023 at 11:04:07AM -0400, Peter Xu wrote: > > > > > It seems vma merging with uffd paths is broken with either > > > > > register/unregister, where right now we can feed wrong parameters to > > > > > vma_merge() and it's found by recent patch which moved asserts upwards in > > > > > vma_merge() by Lorenzo Stoakes: > > > > > > > > > > https://lore.kernel.org/all/ZFunF7DmMdK05MoF@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > > > > > > > > > The problem is in the current code base we didn't fixup "prev" for the case > > > > > where "start" address can be within the "prev" vma section. In that case > > > > > we should have "prev" points to the current vma rather than the previous > > > > > one when feeding to vma_merge(). > > > > > > > > This doesn't seem quite correct, perhaps - "where start is contained within vma > > > > but not clamped to its start. We need to convert this into case 4 which permits > > > > subdivision of prev by assigning vma to prev. As we loop, each subsequent VMA > > > > will be clamped to the start." > > > > > > I think it covers more than case 4 - it can also be case 0 where no merge > > > will happen? > > > > Ugh please let's not call a case that doesn't merge by a number :P but sure of > > course it might also not merge. > > To me the original paragraph was still fine. But if you prefer your version > (which I'm perfectly fine either way if you'd like to spell out what cases > it'll trigger), it'll be: > > It's possible that "start" is contained within vma but not clamped to its > start. We need to convert this into either "cannot merge" case or "can > merge" case 4 which permits subdivision of prev by assigning vma to > prev. As we loop, each subsequent VMA will be clamped to the start. > > Does that look good to you? > Looks good to me, thanks for taking the time! > Thanks, > > -- > Peter Xu >
