Re: [PATCH V15] mm/debug: Add tests validating architecture page table helpers

Qian Cai
2020-03-06T20:44:48Z

On Fri, 2020-03-06 at 05:27 +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.

OK, I get this working on powerpc hash MMU as well, so this?

diff --git a/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
index 64d0f9b15c49..c527d05c0459 100644
--- a/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
+++ b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
@@ -22,8 +22,7 @@
|       nios2: | TODO |
|    openrisc: | TODO |
|      parisc: | TODO |
-    |  powerpc/32: |  ok  |
-    |  powerpc/64: | TODO |
+    |     powerpc: |  ok  |
|       riscv: | TODO |
|        s390: |  ok  |
|          sh: | TODO |
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2e7eee523ba1..176930f40e07 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -116,7 +116,7 @@ config PPC
#
select ARCH_32BIT_OFF_T if PPC32
select ARCH_HAS_DEBUG_VIRTUAL
- select ARCH_HAS_DEBUG_VM_PGTABLE if PPC32
+ select ARCH_HAS_DEBUG_VM_PGTABLE
select ARCH_HAS_DEVMEM_IS_ALLOWED
select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_FORTIFY_SOURCE
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 96a91bda3a85..98990a515268 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -256,7 +256,8 @@ static void __init pte_clear_tests(struct mm_struct *mm,
pte_t *ptep,
pte_t pte = READ_ONCE(*ptep);

pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
- WRITE_ONCE(*ptep, pte);
+ set_pte_at(mm, vaddr, ptep, pte);
+ barrier();
pte_clear(mm, vaddr, ptep);
pte = READ_ONCE(*ptep);
WARN_ON(!pte_none(pte));