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Wed, 2 Sep 2020 03:23:30 +0000 (GMT) Received: from skywalker.linux.ibm.com (unknown [9.199.61.124]) by b03ledav004.gho.boulder.ibm.com (Postfix) with ESMTP; Wed, 2 Sep 2020 03:23:30 +0000 (GMT) X-Mailer: emacs 27.1 (via feedmail 11-beta-1 I) From: "Aneesh Kumar K.V" To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] powerpc: Fix random segfault when freeing hugetlb range In-Reply-To: References: Date: Wed, 02 Sep 2020 08:53:28 +0530 Message-ID: <875z8weua7.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-09-02_02:2020-09-01,2020-09-02 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 bulkscore=0 malwarescore=0 suspectscore=2 mlxlogscore=999 phishscore=0 lowpriorityscore=0 mlxscore=0 impostorscore=0 adultscore=0 priorityscore=1501 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009020022 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christophe Leroy writes: > The following random segfault is observed from time to time with > map_hugetlb selftest: > > root@localhost:~# ./map_hugetlb 1 19 > 524288 kB hugepages > Mapping 1 Mbytes > Segmentation fault > > [ 31.219972] map_hugetlb[365]: segfault (11) at 117 nip 77974f8c lr 779a6834 code 1 in ld-2.23.so[77966000+21000] > [ 31.220192] map_hugetlb[365]: code: 9421ffc0 480318d1 93410028 90010044 9361002c 93810030 93a10034 93c10038 > [ 31.220307] map_hugetlb[365]: code: 93e1003c 93210024 8123007c 81430038 <80e90004> 814a0004 7f443a14 813a0004 > [ 31.221911] BUG: Bad rss-counter state mm:(ptrval) type:MM_FILEPAGES val:33 > [ 31.229362] BUG: Bad rss-counter state mm:(ptrval) type:MM_ANONPAGES val:5 > > This fault is due to hugetlb_free_pgd_range() freeing page tables > that are also used by regular pages. > > As explain in the comment at the beginning of > hugetlb_free_pgd_range(), the verification done in free_pgd_range() > on floor and ceiling is not done here, which means > hugetlb_free_pte_range() can free outside the expected range. > > As the verification cannot be done in hugetlb_free_pgd_range(), it > must be done in hugetlb_free_pte_range(). > Reviewed-by: Aneesh Kumar K.V > Fixes: b250c8c08c79 ("powerpc/8xx: Manage 512k huge pages as standard pages.") > Cc: stable@vger.kernel.org > Signed-off-by: Christophe Leroy > --- > arch/powerpc/mm/hugetlbpage.c | 18 ++++++++++++++++-- > 1 file changed, 16 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c > index 26292544630f..e7ae2a2c4545 100644 > --- a/arch/powerpc/mm/hugetlbpage.c > +++ b/arch/powerpc/mm/hugetlbpage.c > @@ -330,10 +330,24 @@ static void free_hugepd_range(struct mmu_gather *tlb, hugepd_t *hpdp, int pdshif > get_hugepd_cache_index(pdshift - shift)); > } > > -static void hugetlb_free_pte_range(struct mmu_gather *tlb, pmd_t *pmd, unsigned long addr) > +static void hugetlb_free_pte_range(struct mmu_gather *tlb, pmd_t *pmd, > + unsigned long addr, unsigned long end, > + unsigned long floor, unsigned long ceiling) > { > + unsigned long start = addr; > pgtable_t token = pmd_pgtable(*pmd); > > + start &= PMD_MASK; > + if (start < floor) > + return; > + if (ceiling) { > + ceiling &= PMD_MASK; > + if (!ceiling) > + return; > + } > + if (end - 1 > ceiling - 1) > + return; > + We do repeat that for pud/pmd/pte hugetlb_free_range. Can we consolidate that with comment explaining we are checking if the pgtable entry is mapping outside the range? > pmd_clear(pmd); > pte_free_tlb(tlb, token, addr); > mm_dec_nr_ptes(tlb->mm); > @@ -363,7 +377,7 @@ static void hugetlb_free_pmd_range(struct mmu_gather *tlb, pud_t *pud, > */ > WARN_ON(!IS_ENABLED(CONFIG_PPC_8xx)); > > - hugetlb_free_pte_range(tlb, pmd, addr); > + hugetlb_free_pte_range(tlb, pmd, addr, end, floor, ceiling); > > continue; > } > -- > 2.25.0