Re: [PATCH V14] mm/debug: Add tests validating architecture page table helpers
From: Anshuman Khandual
Date: Tue Mar 03 2020 - 00:55:49 EST
On 03/03/2020 01:10 AM, Qian Cai wrote:
> 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 Ã 15:09, Qian Cai a ÃcritÂ:
>>>> 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?
>>>>
>>>> [ÂÂÂ23.263425][ÂÂÂÂT1] debug_vm_pgtable: debug_vm_pgtable: Validating
>>>> architecture page table helpers
>>>> [ÂÂÂ23.263625][ÂÂÂÂT1] ------------[ cut here ]------------
>>>> [ÂÂÂ23.263649][ÂÂÂÂT1] 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 @@
> Â#define RANDOM_ORVALUE GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
> Â#define RANDOM_NZVALUE GENMASK(7, 0)
> Â
> +unsigned long vaddr;
> +
> Âstatic void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
> Â{
> Â pte_t pte = pfn_pte(pfn, prot);
> @@ -256,7 +258,7 @@ static void __init pte_clear_tests(struct mm_struct *mm,
> pte_t *ptep)
> Â
> Â pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
> Â WRITE_ONCE(*ptep, pte);
> - pte_clear(mm, 0, ptep);
> + pte_clear(mm, vaddr, ptep);
> Â pte = READ_ONCE(*ptep);
> Â WARN_ON(!pte_none(pte));
> Â}
> @@ -310,8 +312,9 @@ void __init debug_vm_pgtable(void)
> Â pgtable_t saved_ptep;
> Â pgprot_t prot;
> Â phys_addr_t paddr;
> - unsigned long vaddr, pte_aligned, pmd_aligned;
> + unsigned long pte_aligned, pmd_aligned;
> Â unsigned long pud_aligned, p4d_aligned, pgd_aligned;
> + spinlock_t *ptl;
> Â
> Â pr_info("Validating architecture page table helpers\n");
> Â prot = vm_get_page_prot(VMFLAGS);
> @@ -344,7 +347,7 @@ void __init debug_vm_pgtable(void)
> Â p4dp = p4d_alloc(mm, pgdp, vaddr);
> Â pudp = pud_alloc(mm, p4dp, vaddr);
> Â pmdp = pmd_alloc(mm, pudp, vaddr);
> - ptep = pte_alloc_map(mm, pmdp, vaddr);
> + ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
> Â
> Â /*
> Â Â* Save all the page table page addresses as the page table
> @@ -370,7 +373,7 @@ void __init debug_vm_pgtable(void)
> Â p4d_clear_tests(mm, p4dp);
> Â pgd_clear_tests(mm, pgdp);
> Â
> - pte_unmap(ptep);
> + pte_unmap_unlock(ptep, ptl);
> Â
> Â pmd_populate_tests(mm, pmdp, saved_ptep);
> Â pud_populate_tests(mm, pudp, saved_pmdp);
>
Below is slightly modified version of your change above and should still
prevent the bug on powerpc. Will it be possible for you to re-test this
? Once confirmed, will send a patch enabling this test on powerpc64
keeping your authorship. Thank you.
mm/debug_vm_pgtable.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 96dd7d574cef..c310f52c2b80 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -250,13 +250,14 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
}
#endif
-static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep)
+static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
+ unsigned long vaddr)
{
pte_t pte = READ_ONCE(*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));
}
@@ -302,6 +303,7 @@ static unsigned long __init get_random_vaddr(void)
void __init debug_vm_pgtable(void)
{
struct mm_struct *mm;
+ spinlock_t *uninitialized_var(ptl);
pgd_t *pgdp;
p4d_t *p4dp, *saved_p4dp;
pud_t *pudp, *saved_pudp;
@@ -344,7 +346,7 @@ 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
@@ -364,13 +366,13 @@ void __init debug_vm_pgtable(void)
p4d_basic_tests(p4d_aligned, prot);
pgd_basic_tests(pgd_aligned, prot);
- pte_clear_tests(mm, ptep);
+ pte_clear_tests(mm, ptep, vaddr);
pmd_clear_tests(mm, pmdp);
pud_clear_tests(mm, pudp);
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);
--
2.20.1