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[79.242.59.245]) by smtp.gmail.com with ESMTPSA id f17sm1944177wmf.4.2021.08.31.02.53.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 Aug 2021 02:53:06 -0700 (PDT) To: SeongJae Park , akpm@linux-foundation.org Cc: markubo@amazon.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, SeongJae Park References: <20210827150400.6305-1-sj38.park@gmail.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH] mm/damon/vaddr: Safely walk page table Message-ID: Date: Tue, 31 Aug 2021 11:53:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210827150400.6305-1-sj38.park@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=WNfhS+DM; spf=none (imf02.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 880D77001A08 X-Stat-Signature: ph8nux4ozijg5aaap7b5ixytmms48hks X-HE-Tag: 1630403591-234381 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 27.08.21 17:04, SeongJae Park wrote: > From: SeongJae Park >=20 > Commit d7f647622761 ("mm/damon: implement primitives for the virtual > memory address spaces") of linux-mm[1] tries to find PTE or PMD for > arbitrary virtual address using 'follow_invalidate_pte()' without prope= r > locking[2]. This commit fixes the issue by using another page table > walk function for more general use case under proper locking. >=20 > [1] https://github.com/hnaz/linux-mm/commit/d7f647622761 > [2] https://lore.kernel.org/linux-mm/3b094493-9c1e-6024-bfd5-7eca66399b= 7e@redhat.com >=20 > Fixes: d7f647622761 ("mm/damon: implement primitives for the virtual me= mory address spaces") > Reported-by: David Hildenbrand > Signed-off-by: SeongJae Park > --- > mm/damon/vaddr.c | 81 +++++++++++++++++++++++++++++++++++++++++++----= - > 1 file changed, 74 insertions(+), 7 deletions(-) >=20 > diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c > index 230db7413278..b3677f2ef54b 100644 > --- a/mm/damon/vaddr.c > +++ b/mm/damon/vaddr.c > @@ -8,10 +8,12 @@ > #define pr_fmt(fmt) "damon-va: " fmt > =20 > #include > +#include > #include > #include > #include > #include > +#include > #include > #include > #include > @@ -446,14 +448,69 @@ static void damon_pmdp_mkold(pmd_t *pmd, struct m= m_struct *mm, > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > } > =20 > +struct damon_walk_private { > + pmd_t *pmd; > + pte_t *pte; > + spinlock_t *ptl; > +}; > + > +static int damon_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned lo= ng next, > + struct mm_walk *walk) > +{ > + struct damon_walk_private *priv =3D walk->private; > + > + if (pmd_huge(*pmd)) { > + priv->ptl =3D pmd_lock(walk->mm, pmd); > + if (pmd_huge(*pmd)) { > + priv->pmd =3D pmd; > + return 0; > + } > + spin_unlock(priv->ptl); > + } > + > + if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd))) > + return -EINVAL; > + priv->pte =3D pte_offset_map_lock(walk->mm, pmd, addr, &priv->ptl); > + if (!pte_present(*priv->pte)) { > + pte_unmap_unlock(priv->pte, priv->ptl); > + priv->pte =3D NULL; > + return -EINVAL; > + } > + return 0; > +} > + > +static struct mm_walk_ops damon_walk_ops =3D { > + .pmd_entry =3D damon_pmd_entry, > +}; > + > +int damon_follow_pte_pmd(struct mm_struct *mm, unsigned long addr, > + struct damon_walk_private *private) > +{ > + int rc; > + > + private->pte =3D NULL; > + private->pmd =3D NULL; > + rc =3D walk_page_range(mm, addr, addr + 1, &damon_walk_ops, private); > + if (!rc && !private->pte && !private->pmd) > + return -EINVAL; > + return rc; > +} > + > static void damon_va_mkold(struct mm_struct *mm, unsigned long addr) > { > - pte_t *pte =3D NULL; > - pmd_t *pmd =3D NULL; > + struct damon_walk_private walk_result; > + pte_t *pte; > + pmd_t *pmd; > spinlock_t *ptl; > =20 > - if (follow_invalidate_pte(mm, addr, NULL, &pte, &pmd, &ptl)) > + mmap_write_lock(mm); Can you elaborate why mmap_read_lock() isn't sufficient for your use=20 case? The write mode might heavily affect damon performance and workload=20 impact. Also, I wonder if it wouldn't be much easier and cleaner to just handle=20 it completely in the .pmd_entry callback, instead of returning PMDs,=20 PTEs, LOCKs, ... here. You could have static struct mm_walk_ops damon_mkold_ops =3D { .pmd_entry =3D damon_mkold_pmd_entry, }; and static struct mm_walk_ops damon_young_ops =3D { .pmd_entry =3D damon_young_pmd_entry, }; And then just handle everything completely inside the callback, avoiding=20 having to return locked PTEs, PMDs, .... and instead handling it at a=20 single location. Simply forward the page_sz pointer in the latter case=20 to damon_young_ops. damon_va_mkold()/damon_va_young() would mostly only call=20 walk_page_range() with the right ops and eventually convert some return=20 values. --=20 Thanks, David / dhildenb