Re: [PATCH 3/6] userfaultfd: use userfaultfd_*() helpers instead of open coded flag tests

On Tue, Aug 25, 2026 at 02:19:52PM +0300, Mike Rapoport wrote:

quoted

quoted

+/*
+ * Don't do fault around for WP, RWP or MINOR registered uffd range.  For
+ * MINOR registered range, fault around will be a total disaster and ptes can
+ * be installed without notifications; for WP it should mostly be fine as long
+ * as the fault around checks for pte_none() before the installation, however
+ * to be super safe we just forbid it; for RWP, pre-faulted neighbours would
+ * be indistinguishable from accessed pages in PAGEMAP_SCAN (PAGE_IS_ACCESSED)
+ * and pollute the tracked working set, so each page must be populated by its
+ * own fault.
+ */
+static inline bool uffd_disable_fault_around(struct vm_area_struct *vma)
+{
+	return userfaultfd_minor(vma) || userfaultfd_wp(vma) ||
+	       userfaultfd_rwp(vma);

This is changing the logic.

Before we were testing only the flags, now we have:

static inline bool userfaultfd_rwp(const struct vm_area_struct *vma)
{
	/*
	 * Callers gate PAGE_NONE usage on this; PAGE_NONE is a BUILD_BUG()
	 * without CONFIG_ARCH_HAS_PTE_PROTNONE, so fold to false.
	 */
	if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_PROTNONE))
		return false;
	return vma_test_single_mask(vma, VMA_UFFD_RWP);
}

I.e. adding in a CONFIG_ARCH_HAS_PTE_PROTNONE check.

Without CONFIG_ARCH_HAS_PTE_PROTNONE VMA_UFFD_RWP is hardwired to VM_NONE
so it's functionally the same ;-)

Well then you're explicitly removing logic and not mentioning it anywhere
with a NFC commit.

So please say so in the commit message.

quoted

BTW side-note these:

static inline bool userfaultfd_missing(const struct vm_area_struct *vma)
{
	return vma_test_any_mask(vma, VMA_UFFD_MISSING);
}

static inline bool userfaultfd_wp(const struct vm_area_struct *vma)
{
	return vma_test_any_mask(vma, VMA_UFFD_WP);
}

static inline bool userfaultfd_minor(const struct vm_area_struct *vma)
{
	return vma_test_any_mask(vma, VMA_UFFD_MINOR);
}

Should all use vma_test_single_mask() really :)

These are changed anyway in a later patch.

Yup, but you (potentially) break one of them. Will comment there.

quoted

--
Cheers, Lorenzo

--
Sincerely yours,
Mike.

--
Cheers, Lorenzo