Le 14/03/2024 à 13:53, Peter Xu a écrit : > On Thu, Mar 14, 2024 at 08:45:34AM +0000, Christophe Leroy wrote: >> >> >> Le 13/03/2024 à 22:47, peterx@xxxxxxxxxx a écrit : >>> From: Peter Xu <peterx@xxxxxxxxxx> >>> >>> PowerPC book3s 4K mostly has the same definition on both, except pXd_huge() >>> constantly returns 0 for hash MMUs. As Michael Ellerman pointed out [1], >>> it is safe to check _PAGE_PTE on hash MMUs, as the bit will never be set so >>> it will keep returning false. >>> >>> As a reference, __p[mu]d_mkhuge() will trigger a BUG_ON trying to create >>> such huge mappings for 4K hash MMUs. Meanwhile, the major powerpc hugetlb >>> pgtable walker __find_linux_pte() already used pXd_leaf() to check hugetlb >>> mappings. >>> >>> The goal should be that we will have one API pXd_leaf() to detect all kinds >>> of huge mappings. AFAICT we need to use the pXd_leaf() impl (rather than >>> pXd_huge() ones) to make sure ie. THPs on hash MMU will also return true. >> >> All kinds of huge mappings ? >> >> pXd_leaf() will detect only leaf mappings (like pXd_huge() ). There are >> also huge mappings through hugepd. On powerpc 8xx we have 8M huge pages >> and 512k huge pages. A PGD entry covers 4M so pgd_leaf() won't report >> those huge pages. > > Ah yes, I should always mention this is in the context of leaf huge pages > only. Are the examples you provided all fall into hugepd category? If so > I can reword the commit message, as: On powerpc 8xx, only the 8M huge pages fall into the hugepd case. The 512k hugepages are at PTE level, they are handled more or less like CONT_PTE on ARM. see function set_huge_pte_at() for more context. You can also look at pte_leaf_size() and pgd_leaf_size(). By the way pgd_leaf_size() looks odd because it is called only when pgd_leaf_size() returns true, which never happens for 8M pages. > > As a reference, __p[mu]d_mkhuge() will trigger a BUG_ON trying to > create such huge mappings for 4K hash MMUs. Meanwhile, the major > powerpc hugetlb pgtable walker __find_linux_pte() already used > pXd_leaf() to check leaf hugetlb mappings. > > The goal should be that we will have one API pXd_leaf() to detect > all kinds of huge mappings except hugepd. AFAICT we need to use > the pXd_leaf() impl (rather than pXd_huge() ones) to make sure > ie. THPs on hash MMU will also return true. > > Does this look good to you? > > Thanks, >
