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

[Qian Cai <cai@lca.pw>]

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));