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Tue, 24 Mar 2020 16:19:46 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 02OGJhPk185489; Tue, 24 Mar 2020 16:19:45 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3020.oracle.com with ESMTP id 2yxw6n17rg-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 24 Mar 2020 16:19:45 +0000 Received: from abhmp0014.oracle.com (abhmp0014.oracle.com [141.146.116.20]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 02OGJVTZ018297; Tue, 24 Mar 2020 16:19:31 GMT Received: from [192.168.1.206] (/71.63.128.209) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 24 Mar 2020 09:19:31 -0700 Subject: Re: [PATCH v2] mm/hugetlb: fix a addressing exception caused by huge_pte_offset() To: Jason Gunthorpe Cc: "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" , akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, arei.gonglei@huawei.com, weidong.huang@huawei.com, weifuqiang@huawei.com, kvm@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , Sean Christopherson , stable@vger.kernel.org References: <1582342427-230392-1-git-send-email-longpeng2@huawei.com> <51a25d55-de49-4c0a-c994-bf1a8cfc8638@oracle.com> <20200323160955.GY20941@ziepe.ca> <69055395-e7e5-a8e2-7f3e-f61607149318@oracle.com> <20200323180706.GC20941@ziepe.ca> <88698dd7-eb87-4b0b-7ba7-44ef6eab6a6c@oracle.com> <20200323225225.GF20941@ziepe.ca> <20200324115541.GH20941@ziepe.ca> <98d35563-8af0-2693-7e76-e6435da0bbee@oracle.com> <20200324155552.GK20941@ziepe.ca> From: Mike Kravetz Message-ID: <66583587-ca4f-9847-c173-4a3d7938fec6@oracle.com> Date: Tue, 24 Mar 2020 09:19:29 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200324155552.GK20941@ziepe.ca> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9570 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 adultscore=0 malwarescore=0 mlxscore=0 spamscore=0 mlxlogscore=999 bulkscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003240087 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9570 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 clxscore=1015 lowpriorityscore=0 suspectscore=0 priorityscore=1501 malwarescore=0 mlxscore=0 adultscore=0 phishscore=0 impostorscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003240087 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 3/24/20 8:55 AM, Jason Gunthorpe wrote: > On Tue, Mar 24, 2020 at 08:25:09AM -0700, Mike Kravetz wrote: >> On 3/24/20 4:55 AM, Jason Gunthorpe wrote: >>> Also, since CH moved all the get_user_pages_fast code out of the >>> arch's many/all archs can drop their arch specific version of this >>> routine. This is really just a specialized version of gup_fast's >>> algorithm.. >>> >>> (also the arch versions seem different, why do some return actual >>> ptes, not null?) >> >> Not sure I understand that last question. The return value should be >> a *pte or null. > > I mean the common code ends like this: > > pmd = pmd_offset(pud, addr); > if (sz != PMD_SIZE && pmd_none(*pmd)) > return NULL; > /* hugepage or swap? */ > if (pmd_huge(*pmd) || !pmd_present(*pmd)) > return (pte_t *)pmd; > > return NULL; > > So it always returns a pointer into a PUD or PMD, while say, ppc > in __find_linux_pte() ends like: > > return pte_offset_kernel(&pmd, ea); > > Which is pointing to a PTE Ok, now I understand the question. huge_pte_offset will/should only be called for addresses that are in a vma backed by hugetlb pages. So, pte_offset_kernel() will only return page table type (PUD/PMD/etc) associated with a huge page supported by the particular arch. > So does sparc: > > pmd = pmd_offset(pud, addr); > if (pmd_none(*pmd)) > return NULL; > if (is_hugetlb_pmd(*pmd)) > return (pte_t *)pmd; > return pte_offset_map(pmd, addr); > > Which is even worse because it is leaking a kmap.. > > etc > >> /* >> * huge_pte_offset() - Walk the page table to resolve the hugepage >> * entry at address @addr >> * >> * Return: Pointer to page table or swap entry (PUD or PMD) for > ^^^^^^^^^^^^^^^^^^^ > > Ie the above is not followed by the archs > > I'm also scratching my head that a function that returns a pte_t * > always returns a PUD or PMD. Strange bit of type casting.. Yes, the casting is curious. The casting continues in potential subsequent calls to huge_pte_alloc(). -- Mike Kravetz