If pmd or pud is not set, we may set a wrong page mapping level.
Base knowledge:
1) If we have passed pgd_none() check, then current level is at least
PG_LEVEL_1G.
2) If we have passed pud_large() ||!pud_present() check, then current
level is at least PG_LEVEL_2M.
This patch does not change the behavior when a non-NULL value is
returned.
Let's take bask knowledge 2 as an example.
We know *address* belongs to *pud*, however for some reasons *pmd* is
NULL. For example, this address has no physical pages mapped. What we
could benefit from this patch are below:
1) We can walk memory range easier.
If addressA passed to lookup_address(), and NULL returned. We can pass
addressA + level_to_size(level) to lookup_address() in next loop.
...
if (!pte) {
/* level_to_size has not been implemented in upstream*/
address += level_to_size(level);
continue;
}
...
2) keep same behavior because level is set to PG_LEVEL_4K even when pte
is NULL.
So let *level* meaningful even lookup_address_in_pgd return NULL by
moving the assignment before pud/pmd_offset.
Signed-off-by: Pan Xinhui <[email protected]>
---
arch/x86/mm/pageattr.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 727158c..a887704 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -336,19 +336,19 @@ pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long
address,
if (pgd_none(*pgd))
return NULL;
+ *level = PG_LEVEL_1G;
pud = pud_offset(pgd, address);
if (pud_none(*pud))
return NULL;
- *level = PG_LEVEL_1G;
if (pud_large(*pud) || !pud_present(*pud))
return (pte_t *)pud;
+ *level = PG_LEVEL_2M;
pmd = pmd_offset(pud, address);
if (pmd_none(*pmd))
return NULL;
- *level = PG_LEVEL_2M;
if (pmd_large(*pmd) || !pmd_present(*pmd))
return (pte_t *)pmd;
--
1.9.1
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