On Wed, Dec 6, 2023 at 2:24 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: > > On 05/12/2023 17:54, James Houghton wrote: > > On Tue, Dec 5, 2023 at 6:43 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: > > Thanks for pointing this out. So (1) is definitely a bug. The second > > patch in this series makes it impossible to create such a PTE via > > pte_modify (by forcing sw-dirty PTEs to be hw-dirty as well). > > Yes; I think the second patch should be sufficient; I took a quick look at the > other helpers and I don't see anything else that could get the PTE to the > invalid state. > > I have a series that starts using the contpte bit for (multi-size) THP > opportunistically. This bug will affect that too I think. Your patch #2 will fix > for both hugetlb and my series. I'd rather not apply an equivalent to your patch > #1 because its not quite as straightforward in my code path. But I'm pretty > confident that patch # is all that's needed here. There is no need to apply a patch #1-equivalent for multi-size THPs. :) If multi-size THP has the same problem as HugeTLB, patch #2 will fix it too. I don't think multi-size THP has the equivalent problem -- in fact, I'm not sure how multi-size THP keeps the PTE_DIRTY, PTE_WRITE (DBM), and the PTE_RDONLY bits in sync (they do need to be in-sync with each other when the contiguous bit is being used, right?). I included patch #1 (with cc:stable) because it's a more direct fix for HugeTLB that might be slightly easier to backport. If you think that patch #1 should be dropped and patch #2 should be backported, please let me know. Thanks for the review!
