On Thu, Nov 26, 2020 at 01:42:07PM +0100, Peter Zijlstra wrote: > + pgdp = pgd_offset(mm, addr); > + pgd = READ_ONCE(*pgdp);
I forget how x86-32-PAE maps to Linux's PGD/P4D/PUD/PMD scheme, but according to volume 3, section 4.4.2, PAE paging uses a 64-bit PDE, so whether a PDE is a PGD or a PMD, we're only reading it with READ_ONCE rather than the lockless-retry method used by ptep_get_lockless(). So it's potentially racy? Do we need a pmdp_get_lockless() or pgdp_get_lockless()? [...] > + pmdp = pmd_offset_lockless(pudp, pud, addr); > + pmd = READ_ONCE(*pmdp); > + if (!pmd_present(pmd)) > return 0; > > + if (pmd_leaf(pmd)) > + return pmd_leaf_size(pmd); >
