Hi Anshuman, Thanks for looking into this. See my replies below. > > CONFIG_DEBUG_VM_PGTABLE=y > > CONFIG_PAGE_TABLE_CHECK=y > > CONFIG_PAGE_TABLE_CHECK_ENFORCED=y > > Assuming this is on latest mainline. > > I could enable PAGE_TABLE_CHECK on arm64 after some hacks. It did not build > on the platform otherwise. But enabling DEBUG_VM_PGTABLE afterwards did not > create below mentioned problems. Is the problem x86 specific ? This is not x86 specific problem, but page_table_check does not have support for other arches yet. The arm64 support is on my todo list. The patch for arm64 would look something like this: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d283d422c6c4f0264fe8ecf5ae80036bf73f4594 > > > > > During the boot the following BUG is printed: > > > > [ 7.483050][ T1] debug_vm_pgtable: [debug_vm_pgtable ]: > > Validating architecture page tabs > > [ 7.490930][ T1] ------------[ cut here ]------------ > > [ 7.494926][ T1] kernel BUG at mm/page_table_check.c:194! > > Which BUG() is this ? mm/page_table_check.c:194 on latest mainline .. > > void __page_table_check_pud_clear(struct mm_struct *mm, unsigned long addr, > pud_t pud) <---- It turns out I pasted the backtrace from the modified kernel. Here the snippet of backtrace from the mainline: [ 2.276826] ------------[ cut here ]------------ [ 2.280426] kernel BUG at mm/page_table_check.c:162! [ 2.284118] invalid opcode: 0000 [#1] PREEMPT SMP PTI ... Which corresponds to: 152 void __page_table_check_zero(struct page *page, unsigned int order) 153 { 154 struct page_ext *page_ext = lookup_page_ext(page); 155 int i; 156 157 BUG_ON(!page_ext); 158 for (i = 0; i < (1 << order); i++) { 159 struct page_table_check *ptc = get_page_table_check(page_ext); 160 161 BUG_ON(atomic_read(&ptc->anon_map_count)); 162 BUG_ON(atomic_read(&ptc->file_map_count)); I will update the bug log with the mainline backtrace. > > > [ 7.499172][ T1] invalid opcode: 0000 [#1] PREEMPT SMP KASAN > > [ 7.503610][ T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.16.0+ > > [ 7.508600][ T1] Hardware name: QEMU Standard PC (i440FX + PIIX, > > ... > > > > The entry should be properly removed from the page table before the page > > is released to the free list. > > > > Fixes: a5c3b9ffb0f4 ("mm/debug_vm_pgtable: add tests validating advanced arch page table helpers") > I am not sure whether this really fixes an existing problem. What is detected is that a page that potentially has a PTE entry in a user page table was put on a free list. It is not an issue for this test, but would be an issue if it happened elsewhere. > > > > > Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> > > Reviewed-by: Zi Yan <ziy@xxxxxxxxxx> > > Tested-by: Zi Yan <ziy@xxxxxxxxxx> > > --- > > mm/debug_vm_pgtable.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c > > index a7ac97c76762..db2abd9e415b 100644 > > --- a/mm/debug_vm_pgtable.c > > +++ b/mm/debug_vm_pgtable.c > > @@ -171,6 +171,8 @@ static void __init pte_advanced_tests(struct pgtable_debug_args *args) > > ptep_test_and_clear_young(args->vma, args->vaddr, args->ptep); > > pte = ptep_get(args->ptep); > > WARN_ON(pte_young(pte)); > > + > > + ptep_get_and_clear_full(args->mm, args->vaddr, args->ptep, 1); > > } > > Although I dont see any problem on arm64 after this change. This is because page_table_check does not have support for anything beside x86 at the moment. > > > > > static void __init pte_savedwrite_tests(struct pgtable_debug_args *args) > > Pasha
