On 2024/9/24 16:39, Muchun Song wrote:
On Sep 24, 2024, at 16:33, Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:
On 2024/9/24 16:25, Muchun Song wrote:
On Sep 24, 2024, at 14:11, Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:
In the caller of map_pte(), we may modify the pvmw->pte after acquiring
the pvmw->ptl, so convert it to using pte_offset_map_rw_nolock(). At
this time, the pte_same() check is not performed after the pvmw->ptl held,
so we should get pmdval and do pmd_same() check to ensure the stability of
pvmw->pmd.
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
mm/page_vma_mapped.c | 25 ++++++++++++++++++++-----
1 file changed, 20 insertions(+), 5 deletions(-)
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index ae5cc42aa2087..6410f29b37c1b 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -13,9 +13,11 @@ static inline bool not_found(struct page_vma_mapped_walk *pvmw)
return false;
}
-static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp)
+static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp,
+ spinlock_t **ptlp)
{
pte_t ptent;
+ pmd_t pmdval;
Why declare a new variable? Can’t we use *pmdvalp instead?
It's just a coding habit, both are fine for me.
Agree. But sometime it could make code look a little simpler.
if (pvmw->flags & PVMW_SYNC) {
/* Use the stricter lookup */
@@ -25,6 +27,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp)
return !!pvmw->pte;
}
+again:
/*
* It is important to return the ptl corresponding to pte,
* in case *pvmw->pmd changes underneath us; so we need to
@@ -32,10 +35,11 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp)
* proceeds to loop over next ptes, and finds a match later.
* Though, in most cases, page lock already protects this.
*/
- pvmw->pte = pte_offset_map_nolock(pvmw->vma->vm_mm, pvmw->pmd,
- pvmw->address, ptlp);
+ pvmw->pte = pte_offset_map_rw_nolock(pvmw->vma->vm_mm, pvmw->pmd,
+ pvmw->address, &pmdval, ptlp);
if (!pvmw->pte)
return false;
+ *pmdvalp = pmdval;
For instance, here, it is unnecessary if pmdvalp is passed directly to
pte_offset_map_rw_nolock.
OK, will use pmdvalp directly. ;)
ptent = ptep_get(pvmw->pte);
@@ -67,8 +71,13 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp)
} else if (!pte_present(ptent)) {
return false;
}
+ spin_lock(*ptlp);
+ if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pvmw->pmd)))) {
+ pte_unmap_unlock(pvmw->pte, *ptlp);
+ goto again;
+ }
pvmw->ptl = *ptlp;
- spin_lock(pvmw->ptl);
+
return true;
}
@@ -278,7 +287,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
step_forward(pvmw, PMD_SIZE);
continue;
}
- if (!map_pte(pvmw, &ptl)) {
+ if (!map_pte(pvmw, &pmde, &ptl)) {
if (!pvmw->pte)
goto restart;
goto next_pte;
@@ -307,6 +316,12 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
if (!pvmw->ptl) {
pvmw->ptl = ptl;
spin_lock(pvmw->ptl);
+ if (unlikely(!pmd_same(pmde, pmdp_get_lockless(pvmw->pmd)))) {
+ pte_unmap_unlock(pvmw->pte, pvmw->ptl);
+ pvmw->ptl = NULL;
+ pvmw->pte = NULL;
+ goto restart;
+ }
}
goto this_pte;
} while (pvmw->address < end);
--
2.20.1
