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Thu, 19 Mar 2020 03:56:45 +0000 Received: from b01ledav004.gho.pok.ibm.com (b01ledav004.gho.pok.ibm.com [9.57.199.109]) by b01cxnp22033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 02J3ug0O45285652 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 19 Mar 2020 03:56:42 GMT Received: from b01ledav004.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 45A32112066; Thu, 19 Mar 2020 03:56:42 +0000 (GMT) Received: from b01ledav004.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D9C28112062; Thu, 19 Mar 2020 03:56:38 +0000 (GMT) Received: from skywalker.ibmuc.com (unknown [9.199.34.213]) by b01ledav004.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 19 Mar 2020 03:56:38 +0000 (GMT) From: "Aneesh Kumar K.V" To: linuxppc-dev@lists.ozlabs.org, mpe@ellerman.id.au, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org Cc: npiggin@gmail.com, paulus@ozlabs.org, leonardo@linux.ibm.com, kirill@shutemov.name, "Aneesh Kumar K.V" , Mahesh Salgaonkar Subject: [PATCH v2 06/22] powerpc/mce: Don't reload pte val in addr_to_pfn Date: Thu, 19 Mar 2020 09:25:53 +0530 Message-Id: <20200319035609.158654-7-aneesh.kumar@linux.ibm.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200319035609.158654-1-aneesh.kumar@linux.ibm.com> References: <20200319035609.158654-1-aneesh.kumar@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.645 definitions=2020-03-18_10:2020-03-18,2020-03-18 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 spamscore=0 suspectscore=0 mlxlogscore=794 priorityscore=1501 impostorscore=0 phishscore=0 clxscore=1015 adultscore=0 malwarescore=0 bulkscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003190013 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: A lockless page table walk should be safe against parallel THP collapse, = THP split and madvise(MADV_DONTNEED)/parallel fault. This patch makes sure ke= rnel won't reload the pteval when checking for different conditions. The patch= also added a check for pte_present to make sure the kernel is indeed operating on a PTE and not a pointer to level 0 table page. The pfn value we find here can be different from the actual pfn on which machine check happened. This can happen if we raced with a parallel updat= e of the page table. In such a scenario we end up isolating a wrong pfn. Bu= t that doesn't have any other side effect. Cc: Mahesh Salgaonkar Signed-off-by: Aneesh Kumar K.V --- arch/powerpc/kernel/mce_power.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_po= wer.c index 1cbf7f1a4e3d..c1580fcf95ea 100644 --- a/arch/powerpc/kernel/mce_power.c +++ b/arch/powerpc/kernel/mce_power.c @@ -27,7 +27,7 @@ */ unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr) { - pte_t *ptep; + pte_t *ptep, pte; unsigned int shift; unsigned long pfn, flags; struct mm_struct *mm; @@ -39,19 +39,23 @@ unsigned long addr_to_pfn(struct pt_regs *regs, unsig= ned long addr) =20 local_irq_save(flags); ptep =3D __find_linux_pte(mm->pgd, addr, NULL, &shift); + if (!ptep) { + pfn =3D ULONG_MAX; + goto out; + } + pte =3D READ_ONCE(*ptep); =20 - if (!ptep || pte_special(*ptep)) { + if (!pte_present(pte) || pte_special(pte)) { pfn =3D ULONG_MAX; goto out; } =20 if (shift <=3D PAGE_SHIFT) - pfn =3D pte_pfn(*ptep); + pfn =3D pte_pfn(pte); else { unsigned long rpnmask =3D (1ul << shift) - PAGE_SIZE; - pfn =3D pte_pfn(__pte(pte_val(*ptep) | (addr & rpnmask))); + pfn =3D pte_pfn(__pte(pte_val(pte) | (addr & rpnmask))); } - out: local_irq_restore(flags); return pfn; --=20 2.24.1