On 9/1/20 1:08 PM, Anshuman Khandual wrote:

On 09/01/2020 12:07 PM, Aneesh Kumar K.V wrote:

quoted

On 9/1/20 8:55 AM, Anshuman Khandual wrote:

quoted

On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:

quoted

pte_clear_tests operate on an existing pte entry. Make sure that is not a none
pte entry.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
   mm/debug_vm_pgtable.c | 6 ++++--
   1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 21329c7d672f..8527ebb75f2c 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c

@@ -546,7 +546,7 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
   static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
                      unsigned long vaddr)
   {
-    pte_t pte = ptep_get(ptep);
+    pte_t pte =  ptep_get_and_clear(mm, vaddr, ptep);

Seems like ptep_get_and_clear() here just clears the entry in preparation
for a following set_pte_at() which otherwise would have been a problem on
ppc64 as you had pointed out earlier i.e set_pte_at() should not update an
existing valid entry. So the commit message here is bit misleading.

and also fetch the pte value which is used further.

quoted

quoted

         pr_debug("Validating PTE clear\n");
       pte = __pte(pte_val(pte) | RANDOM_ORVALUE);

@@ -944,7 +944,7 @@ static int __init debug_vm_pgtable(void)
       p4d_t *p4dp, *saved_p4dp;
       pud_t *pudp, *saved_pudp;
       pmd_t *pmdp, *saved_pmdp, pmd;
-    pte_t *ptep;
+    pte_t *ptep, pte;
       pgtable_t saved_ptep;
       pgprot_t prot, protnone;
       phys_addr_t paddr;

@@ -1049,6 +1049,8 @@ static int __init debug_vm_pgtable(void)
        */
         ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
+    pte = pfn_pte(pte_aligned, prot);
+    set_pte_at(mm, vaddr, ptep, pte);

Not here, creating and populating an entry must be done in respective
test functions itself. Besides, this seems bit redundant as well. The
test pte_clear_tests() with the above change added, already

- Clears the PTEP entry with ptep_get_and_clear()

and fetch the old value set previously.

In that case, please move above two lines i.e

pte = pfn_pte(pte_aligned, prot);
set_pte_at(mm, vaddr, ptep, pte);

from debug_vm_pgtable() to pte_clear_tests() and update it's arguments
as required.

Frankly, I don't understand what these tests are testing. It all looks 
like some random clear and set.

static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
				   unsigned long vaddr, unsigned long pfn,
				   pgprot_t prot)
{

	pte_t pte = pfn_pte(pfn, prot);
	set_pte_at(mm, vaddr, ptep, pte);

	pte =  ptep_get_and_clear(mm, vaddr, ptep);

	pr_debug("Validating PTE clear\n");
	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
	set_pte_at(mm, vaddr, ptep, pte);
	barrier();
	pte_clear(mm, vaddr, ptep);
	pte = ptep_get(ptep);
	WARN_ON(!pte_none(pte));
}


-aneesh