From mboxrd@z Thu Jan 1 00:00:00 1970 From: Prakash Sangappa Subject: Re: [RFC PATCH] Add /proc//numa_vamaps for numa node information Date: Fri, 14 Sep 2018 11:07:53 -0700 Message-ID: References: <2ce01d91-5fba-b1b7-2956-c8cc1853536d@intel.com> <33f96879-351f-674a-ca23-43f233f4eb1d@linux.vnet.ibm.com> <82d2b35c-272a-ad02-692f-2c109aacdfb6@oracle.com> <8569dabb-4930-aa20-6249-72457e2df51e@intel.com> <51145ccb-fc0d-0281-9757-fb8a5112ec24@oracle.com> <94ee0b6c-4663-0705-d4a8-c50342f6b483@oracle.com> <20180914062132.GI20287@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Jann Horn , Michal Hocko Cc: Dave Hansen , Anshuman Khandual , Andrew Morton , kernel list , Linux-MM , Linux API , "Kirill A . Shutemov" , n-horiguchi@ah.jp.nec.com, Ulrich Drepper , David Rientjes , Horiguchi Naoya , steven.sistare@oracle.com List-Id: linux-api@vger.kernel.org On 9/14/18 5:49 AM, Jann Horn wrote: > On Fri, Sep 14, 2018 at 8:21 AM Michal Hocko wrote: >> On Fri 14-09-18 03:33:28, Jann Horn wrote: >>> On Wed, Sep 12, 2018 at 10:43 PM prakash.sangappa >>> wrote: >>>> On 05/09/2018 04:31 PM, Dave Hansen wrote: >>>>> On 05/07/2018 06:16 PM, prakash.sangappa wrote: >>>>>> It will be /proc//numa_vamaps. Yes, the behavior will be >>>>>> different with respect to seeking. Output will still be text and >>>>>> the format will be same. >>>>>> >>>>>> I want to get feedback on this approach. >>>>> I think it would be really great if you can write down a list of the >>>>> things you actually want to accomplish. Dare I say: you need a >>>>> requirements list. >>>>> >>>>> The numa_vamaps approach continues down the path of an ever-growing list >>>>> of highly-specialized /proc/ files. I don't think that is >>>>> sustainable, even if it has been our trajectory for many years. >>>>> >>>>> Pagemap wasn't exactly a shining example of us getting new ABIs right, >>>>> but it sounds like something along those is what we need. >>>> Just sent out a V2 patch. This patch simplifies the file content. It >>>> only provides VA range to numa node id information. >>>> >>>> The requirement is basically observability for performance analysis. >>>> >>>> - Need to be able to determine VA range to numa node id information. >>>> Which also gives an idea of which range has memory allocated. >>>> >>>> - The proc file /proc//numa_vamaps is in text so it is easy to >>>> directly view. >>>> >>>> The V2 patch supports seeking to a particular process VA from where >>>> the application could read the VA to numa node id information. >>>> >>>> Also added the 'PTRACE_MODE_READ_REALCREDS' check when opening the >>>> file /proc file as was indicated by Michal Hacko >>> procfs files should use PTRACE_MODE_*_FSCREDS, not PTRACE_MODE_*_REALCREDS. >> Out of my curiosity, what is the semantic difference? At least >> kernel_move_pages uses PTRACE_MODE_READ_REALCREDS. Is this a bug? > No, that's fine. REALCREDS basically means "look at the caller's real > UID for the access check", while FSCREDS means "look at the caller's > filesystem UID". The ptrace access check has historically been using > the real UID, which is sorta weird, but normally works fine. Given > that this is documented, I didn't see any reason to change it for most > things that do ptrace access checks, even if the EUID would IMO be > more appropriate. But things that capture caller credentials at points > like open() really shouldn't look at the real UID; instead, they > should use the filesystem UID (which in practice is basically the same > as the EUID). > > So in short, it depends on the interface you're coming through: Direct > syscalls use REALCREDS, things that go through the VFS layer use > FSCREDS. So in this case can the REALCREDS check be done in the read() system call when reading the /proc file instead of the open call?