From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 533B0C25B0D for ; Wed, 10 Aug 2022 08:45:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231777AbiHJIpU (ORCPT ); Wed, 10 Aug 2022 04:45:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40888 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230104AbiHJIpT (ORCPT ); Wed, 10 Aug 2022 04:45:19 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E44221ADA5; Wed, 10 Aug 2022 01:45:16 -0700 (PDT) Received: from [192.168.10.7] (unknown [39.45.206.166]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id 7B0486601BE2; Wed, 10 Aug 2022 09:45:06 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1660121114; bh=1473869Iv8iu6o+SiEUIxAN5ZWzArP8lHuuYZHC8TEQ=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=VOT3kbYiY90iOsNmwjPKDRcrnhA+Nq+dHr2wUdQ3dp9YXfPoB45lsModbPKyApHkC FqBlOolHNZDE+WjJGbgYXMW9exPj0qxxJb+ixSAn890nshpejAJA9F3VE931As8+sK x6005gi8H2dMEftgItMtJpNFHI5E0rwISEYaEmkXVeTFZsMdGLpUv/fZqScFXLHSxt PrF69uDmhxQOiOzlllAlwWiKiu/Fnpy2Sm4c8YBdhu2x/lEV3arOPAJ+3fOIT9prrM lCuNUMzEy2M93qUld/dgvNQf3T9IPenUsGD5zceoYOZ52JX0DIPo7GXaVwqTNv8Pbd 48dFgrtPO/2BQ== Message-ID: Date: Wed, 10 Aug 2022 13:45:00 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Cc: usama.anjum@collabora.com, kernel@collabora.com Subject: Re: [PATCH 0/5] Add process_memwatch syscall Content-Language: en-US To: Jonathan Corbet , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "H. Peter Anvin" , Arnd Bergmann , Andrew Morton , Peter Zijlstra , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Shuah Khan , "open list:DOCUMENTATION" , open list , "open list:PROC FILESYSTEM" , "open list:ABI/API" , "open list:GENERIC INCLUDE/ASM HEADER FILES" , "open list:MEMORY MANAGEMENT" , "open list:PERFORMANCE EVENTS SUBSYSTEM" , "open list:KERNEL SELFTEST FRAMEWORK" , krisman@collabora.com References: <20220726161854.276359-1-usama.anjum@collabora.com> From: Muhammad Usama Anjum In-Reply-To: <20220726161854.276359-1-usama.anjum@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On 7/26/22 9:18 PM, Muhammad Usama Anjum wrote: > Hello, > > This patch series implements a new syscall, process_memwatch. Currently, > only the support to watch soft-dirty PTE bit is added. This syscall is > generic to watch the memory of the process. There is enough room to add > more operations like this to watch memory in the future. > > Soft-dirty PTE bit of the memory pages can be viewed by using pagemap > procfs file. The soft-dirty PTE bit for the memory in a process can be > cleared by writing to the clear_refs file. This series adds features that > weren't possible through the Proc FS interface. > - There is no atomic get soft-dirty PTE bit status and clear operation > possible. > - The soft-dirty PTE bit of only a part of memory cannot be cleared. > > Historically, soft-dirty PTE bit tracking has been used in the CRIU > project. The Proc FS interface is enough for that as I think the process > is frozen. We have the use case where we need to track the soft-dirty > PTE bit for running processes. We need this tracking and clear mechanism > of a region of memory while the process is running to emulate the > getWriteWatch() syscall of Windows. This syscall is used by games to keep > track of dirty pages and keep processing only the dirty pages. This > syscall can be used by the CRIU project and other applications which > require soft-dirty PTE bit information. > > As in the current kernel there is no way to clear a part of memory (instead > of clearing the Soft-Dirty bits for the entire processi) and get+clear > operation cannot be performed atomically, there are other methods to mimic > this information entirely in userspace with poor performance: > - The mprotect syscall and SIGSEGV handler for bookkeeping > - The userfaultfd syscall with the handler for bookkeeping > > long process_memwatch(int pidfd, unsigned long start, int len, > unsigned int flags, void *vec, int vec_len); Any thoughts? > > This syscall can be used by the CRIU project and other applications which > require soft-dirty PTE bit information. The following operations are > supported in this syscall: > - Get the pages that are soft-dirty. > - Clear the pages which are soft-dirty. > - The optional flag to ignore the VM_SOFTDIRTY and only track per page > soft-dirty PTE bit > > There are two decisions which have been taken about how to get the output > from the syscall. > - Return offsets of the pages from the start in the vec > - Stop execution when vec is filled with dirty pages > These two arguments doesn't follow the mincore() philosophy where the > output array corresponds to the address range in one to one fashion, hence > the output buffer length isn't passed and only a flag is set if the page > is present. This makes mincore() easy to use with less control. We are > passing the size of the output array and putting return data consecutively > which is offset of dirty pages from the start. The user can convert these > offsets back into the dirty page addresses easily. Suppose, the user want > to get first 10 dirty pages from a total memory of 100 pages. He'll > allocate output buffer of size 10 and process_memwatch() syscall will > abort after finding the 10 pages. This behaviour is needed to support > Windows' getWriteWatch(). The behaviour like mincore() can be achieved by > passing output buffer of 100 size. This interface can be used for any > desired behaviour. > > Regards, > Muhammad Usama Anjum > > Muhammad Usama Anjum (5): > fs/proc/task_mmu: make functions global to be used in other files > mm: Implement process_memwatch syscall > mm: wire up process_memwatch syscall for x86 > selftests: vm: add process_memwatch syscall tests > mm: add process_memwatch syscall documentation > > Documentation/admin-guide/mm/soft-dirty.rst | 48 +- > arch/x86/entry/syscalls/syscall_32.tbl | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > fs/proc/task_mmu.c | 84 +-- > include/linux/mm_inline.h | 99 +++ > include/linux/syscalls.h | 3 +- > include/uapi/asm-generic/unistd.h | 5 +- > include/uapi/linux/memwatch.h | 12 + > kernel/sys_ni.c | 1 + > mm/Makefile | 2 +- > mm/memwatch.c | 285 ++++++++ > tools/include/uapi/asm-generic/unistd.h | 5 +- > .../arch/x86/entry/syscalls/syscall_64.tbl | 1 + > tools/testing/selftests/vm/.gitignore | 1 + > tools/testing/selftests/vm/Makefile | 2 + > tools/testing/selftests/vm/memwatch_test.c | 635 ++++++++++++++++++ > 16 files changed, 1098 insertions(+), 87 deletions(-) > create mode 100644 include/uapi/linux/memwatch.h > create mode 100644 mm/memwatch.c > create mode 100644 tools/testing/selftests/vm/memwatch_test.c > -- Muhammad Usama Anjum