On Wed, 2020-02-26 at 10:51 -0500, Qian Cai wrote: > On Wed, 2020-02-26 at 15:45 +0100, Christophe Leroy wrote: > > > > Le 26/02/2020 à 15:09, Qian Cai a écrit : > > > On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote: > > > > This adds tests which will validate architecture page table helpers and > > > > other accessors in their compliance with expected generic MM semantics. > > > > This will help various architectures in validating changes to existing > > > > page table helpers or addition of new ones. > > > > > > > > This test covers basic page table entry transformations including but > > > > not > > > > limited to old, young, dirty, clean, write, write protect etc at various > > > > level along with populating intermediate entries with next page table > > > > page > > > > and validating them. > > > > > > > > Test page table pages are allocated from system memory with required > > > > size > > > > and alignments. The mapped pfns at page table levels are derived from a > > > > real pfn representing a valid kernel text symbol. This test gets called > > > > inside kernel_init() right after async_synchronize_full(). > > > > > > > > This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. > > > > Any > > > > architecture, which is willing to subscribe this test will need to > > > > select > > > > ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, > > > > s390 > > > > and ppc32 platforms where the test is known to build and run > > > > successfully. > > > > Going forward, other architectures too can subscribe the test after > > > > fixing > > > > any build or runtime problems with their page table helpers. Meanwhile > > > > for > > > > better platform coverage, the test can also be enabled with > > > > CONFIG_EXPERT > > > > even without ARCH_HAS_DEBUG_VM_PGTABLE. > > > > > > > > Folks interested in making sure that a given platform's page table > > > > helpers > > > > conform to expected generic MM semantics should enable the above config > > > > which will just trigger this test during boot. Any non conformity here > > > > will > > > > be reported as an warning which would need to be fixed. This test will > > > > help > > > > catch any changes to the agreed upon semantics expected from generic MM > > > > and > > > > enable platforms to accommodate it thereafter. > > > > > > How useful is this that straightly crash the powerpc? > > > > > > [ 23.263425][ T1] debug_vm_pgtable: debug_vm_pgtable: Validating > > > architecture page table helpers > > > [ 23.263625][ T1] ------------[ cut here ]------------ > > > [ 23.263649][ T1] kernel BUG at arch/powerpc/mm/pgtable.c:274! > > > > The problem on PPC64 is known and has to be investigated and fixed. > > It might be interesting to hear what powerpc64 maintainers would say about it > and if it is actually worth "fixing" in the arch code, but that BUG_ON() was > there since 2009 and had not been exposed until this patch comes alone?
This patch below makes it works on powerpc64 in order to dodge the BUG_ON()s in assert_pte_locked() triggered by pte_clear_tests(). diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c index 96dd7d574cef..50b385233971 100644 --- a/mm/debug_vm_pgtable.c +++ b/mm/debug_vm_pgtable.c @@ -55,6 +55,8 @@ #define RANDOM_ORVALUE GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS) #define RANDOM_NZVALUE GENMASK(7, 0) +unsigned long vaddr; + static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot) { pte_t pte = pfn_pte(pfn, prot); @@ -256,7 +258,7 @@ static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep) pte = __pte(pte_val(pte) | RANDOM_ORVALUE); WRITE_ONCE(*ptep, pte); - pte_clear(mm, 0, ptep); + pte_clear(mm, vaddr, ptep); pte = READ_ONCE(*ptep); WARN_ON(!pte_none(pte)); } @@ -310,8 +312,9 @@ void __init debug_vm_pgtable(void) pgtable_t saved_ptep; pgprot_t prot; phys_addr_t paddr; - unsigned long vaddr, pte_aligned, pmd_aligned; + unsigned long pte_aligned, pmd_aligned; unsigned long pud_aligned, p4d_aligned, pgd_aligned; + spinlock_t *ptl; pr_info("Validating architecture page table helpers\n"); prot = vm_get_page_prot(VMFLAGS); @@ -344,7 +347,7 @@ void __init debug_vm_pgtable(void) p4dp = p4d_alloc(mm, pgdp, vaddr); pudp = pud_alloc(mm, p4dp, vaddr); pmdp = pmd_alloc(mm, pudp, vaddr); - ptep = pte_alloc_map(mm, pmdp, vaddr); + ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl); /* * Save all the page table page addresses as the page table @@ -370,7 +373,7 @@ void __init debug_vm_pgtable(void) p4d_clear_tests(mm, p4dp); pgd_clear_tests(mm, pgdp); - pte_unmap(ptep); + pte_unmap_unlock(ptep, ptl); pmd_populate_tests(mm, pmdp, saved_ptep); pud_populate_tests(mm, pudp, saved_pmdp);