On Fri, May 29, 2026 at 08:24:55AM +0100, Lorenzo Stoakes wrote: > On Tue, May 26, 2026 at 02:04:56PM +0100, Kiryl Shutsemau wrote: > > From: "Kiryl Shutsemau (Meta)" <[email protected]> > > > > Preparatory patch for userfaultfd read-write protection (RWP). RWP > > extends userfaultfd protection from plain write-protection (WP) to > > full read-write protection: accesses to an RWP-protected range -- > > reads as well as writes -- trap through userfaultfd. > > > > Reserve VM_UFFD_RWP, add the userfaultfd_rwp() and > > userfaultfd_protected() helpers, and wire up the smaps "ur" entry and > > the trace-flag table the rest of the series will use. The flag is > > gated on CONFIG_USERFAULTFD_RWP, which is introduced together with the > > UAPI in a later patch; until then VM_UFFD_RWP aliases VM_NONE and > > every downstream check folds to dead code. > > > > Nothing sets or queries the flag yet. > > > > Signed-off-by: Kiryl Shutsemau <[email protected]> > > Assisted-by: Claude:claude-opus-4-6 > > Hm, if you've just used claude to bounce ideas off, I'm really not sure if > it's necessary to disclose, though I respect your thoroughness for doing so > :)
I've elaborated on how I used Claude in reply to Andrew: https://lore.kernel.org/all/af5eALk9yO8pPcHv@thinkstation It is more than bouncing ideas. > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index 71b11945e4fc..6499cfb61dc4 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -362,6 +362,7 @@ enum { > > #endif > > DECLARE_VMA_BIT(UFFD_MINOR, 41), > > DECLARE_VMA_BIT(SEALED, 42), > > + DECLARE_VMA_BIT(UFFD_RWP, 43), > > I'm guessing CONFIG_USERFAULTFD_RWP is predicated on CONFIG_64BIT? Yes: depends on 64BIT && ARCH_HAS_PTE_PROTNONE && HAVE_ARCH_USERFAULTFD_WP > > It's a silly situation and once my VMA flags stuff is done it'll be > eliminated but for now... :) Yeah. I actually would appreciate your take on 04/18. It is related. > > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > > index f4cf5763f92c..0aef628514df 100644 > > --- a/include/linux/userfaultfd_k.h > > +++ b/include/linux/userfaultfd_k.h > > @@ -21,10 +21,11 @@ > > #include <linux/hugetlb_inline.h> > > > > /* The set of all possible UFFD-related VM flags. */ > > -#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_WP | VM_UFFD_MINOR) > > +#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_MINOR | \ > > + VM_UFFD_WP | VM_UFFD_RWP) > > > > #define __VMA_UFFD_FLAGS mk_vma_flags(VMA_UFFD_MISSING_BIT, > > VMA_UFFD_WP_BIT, \ > > - VMA_UFFD_MINOR_BIT) > > + VMA_UFFD_MINOR_BIT, VMA_UFFD_RWP_BIT) > > > > /* > > * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining > > @@ -178,7 +179,7 @@ static inline bool > > is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma, > > */ > > static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma) > > { > > - return vma->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR); > > + return vma->vm_flags & (VM_UFFD_MINOR | VM_UFFD_WP | VM_UFFD_RWP); > > While we're here we might as well switch to using the new API? > > Can do: > > return vma_test_any_mask(vma, __VMA_UFFD_FLAGS); > > One unfortunate thing is using bit values means we can't do the VM_NONE > trick, but if !CONFIG_USERFAULTFD_RWP then VMA_UFFD_RWP_BIT wouldn't be set > anyway, same for minor so this should be fine? I think we need to decide first if the 04/18 direction is right. We can define VMA_UFFD_RWP_BIT to VMA_NO_BIT if !CONFIG_USERFAULTFD_RWP. > > } > > > > /* > > @@ -208,6 +209,16 @@ static inline bool userfaultfd_minor(struct > > vm_area_struct *vma) > > return vma->vm_flags & VM_UFFD_MINOR; > > } > > > > +static inline bool userfaultfd_rwp(struct vm_area_struct *vma) > > +{ > > + return vma->vm_flags & VM_UFFD_RWP; > > +} > > Can be: > > return vma_test(vma, VMA_UFFD_RWP_BIT); Yep. -- Kiryl Shutsemau / Kirill A. Shutemov
