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From: Muchun Song X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: Mime-Version: 1.0 (1.0) Subject: Re: [PATCH v4 10/13] mm: page_vma_mapped_walk: map_pte() use pte_offset_map_rw_nolock() Date: Tue, 24 Sep 2024 16:25:06 +0800 Message-Id: References: Cc: david@redhat.com, hughd@google.com, willy@infradead.org, vbabka@kernel.org, akpm@linux-foundation.org, rppt@kernel.org, vishal.moola@gmail.com, peterx@redhat.com, ryan.roberts@arm.com, christophe.leroy2@cs-soprasteria.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org In-Reply-To: To: Qi Zheng X-Migadu-Flow: FLOW_OUT > On Sep 24, 2024, at 14:11, Qi Zheng wrote: >=20 > =EF=BB=BFIn the caller of map_pte(), we may modify the pvmw->pte after acq= uiring > 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. >=20 > Signed-off-by: Qi Zheng > --- > mm/page_vma_mapped.c | 25 ++++++++++++++++++++----- > 1 file changed, 20 insertions(+), 5 deletions(-) >=20 > 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_wal= k *pvmw) > return false; > } >=20 > -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=E2=80=99t we use *pmdvalp instead? >=20 > if (pvmw->flags & PVMW_SYNC) { > /* Use the stricter lookup */ > @@ -25,6 +27,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, s= pinlock_t **ptlp) > return !!pvmw->pte; > } >=20 > +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 =3D pte_offset_map_nolock(pvmw->vma->vm_mm, pvmw->pmd, > - pvmw->address, ptlp); > + pvmw->pte =3D pte_offset_map_rw_nolock(pvmw->vma->vm_mm, pvmw->pmd, > + pvmw->address, &pmdval, ptlp); > if (!pvmw->pte) > return false; > + *pmdvalp =3D pmdval; >=20 > ptent =3D ptep_get(pvmw->pte); >=20 > @@ -67,8 +71,13 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, s= pinlock_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 =3D *ptlp; > - spin_lock(pvmw->ptl); > + > return true; > } >=20 > @@ -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 =3D ptl; > spin_lock(pvmw->ptl); > + if (unlikely(!pmd_same(pmde, pmdp_get_lockless(pvmw->pmd)))) {= > + pte_unmap_unlock(pvmw->pte, pvmw->ptl); > + pvmw->ptl =3D NULL; > + pvmw->pte =3D NULL; > + goto restart; > + } > } > goto this_pte; > } while (pvmw->address < end); > -- > 2.20.1 >=20