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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 63DB4C05027 for ; Thu, 2 Feb 2023 10:15:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F34B96B0071; Thu, 2 Feb 2023 05:15:51 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id EE47B6B0072; Thu, 2 Feb 2023 05:15:51 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DABF66B0078; Thu, 2 Feb 2023 05:15:51 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id CCA4A6B0071 for ; Thu, 2 Feb 2023 05:15:51 -0500 (EST) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 98EA314080A for ; Thu, 2 Feb 2023 10:15:51 +0000 (UTC) X-FDA: 80421945702.13.F00B578 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by imf08.hostedemail.com (Postfix) with ESMTP id A2C7B160002 for ; Thu, 2 Feb 2023 10:15:48 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=THhg5wHa; spf=pass (imf08.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com; dmarc=pass (policy=reject) header.from=collabora.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1675332949; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=L19tboZLiqXtL1TfFJhOWR/KlM5mnWYT9kmA9WSQ5n0=; b=KtFkaQLtKOLhOupatrZNih+0T5AzfN9qdHHf0G2szrjgVt5SXAMf+EKxvbx4ptJuZSWUf6 Jdbkw+tedDZIXk7rGCMOL6gS1Yya1zu4xgCfb4XJc2yNeMRjyDBhfHxzf9iOp26KL/21MK LjrKBWELx6kjqOtCeuogehiKBSplL3s= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=THhg5wHa; spf=pass (imf08.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com; dmarc=pass (policy=reject) header.from=collabora.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1675332949; a=rsa-sha256; cv=none; b=inXy9acshxBYsdOiZWPNmoQj0gJoZ9+q4NMnuAf7i55pluepAsscIK/mkvjSrFuGjD4X1C QGq6XJSJiUtxbMKWg+SFG6w9E8ccNsFdWnfVEjhfpREkyJdrSCRPzQjimmOnqI9ZaWA0hK VUd2kdftwijBa7Z/kblo3IV663MWb5M= Received: from [192.168.10.12] (unknown [39.45.165.226]) (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 8A3F16602ED8; Thu, 2 Feb 2023 10:15:40 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1675332947; bh=8D7MeiVWI14xWAZXvOCJFfJ27Ec1rl7w6HG/K7x0riI=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=THhg5wHabY3dGvNSFKIEM/zUshZLGuHQsmdhkj1oZlSwaS9v1E1cg5OXMBwJEzHeB vpj1BgO7HoRHy5l3YOZ/hUKIf+b+0opWxKJ0iNUZEJt4tkUsfcgOfFm6xFo0l+191/ 7ZMFSAmUdemsEmQ8vc2PDLCugxChgMuCNhZYT44qkNmJgKXoBhLJDCT33dmETxQnev fTSMM0AZEZU+C7EUzDtjaK82mYpJ6tXRgIBPhYtyrgs/3Sdh6I7WDIyHN4opLbTKma LyrQrNHa+q5JnOOTWRB0JAlvsj+yVusYVPswcpOhgObELGFcyO6jR2qemZpjnmyt46 b6tihO3urAZ/g== Message-ID: <02f0eab8-6fb7-74c9-4bfa-1c4c50944cc2@collabora.com> Date: Thu, 2 Feb 2023 15:15:37 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Cc: Muhammad Usama Anjum , David Hildenbrand , Andrew Morton , =?UTF-8?B?TWljaGHFgiBNaXJvc8WC?= =?UTF-8?Q?aw?= , Andrei Vagin , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Matthew Wilcox , Pasha Tatashin , Mike Rapoport , Nadav Amit , Axel Rasmussen , "Gustavo A . R . Silva" , Dan Williams , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Greg KH , kernel@collabora.com Subject: Re: [PATCH v9 1/3] userfaultfd: Add UFFD WP Async support Content-Language: en-US To: Peter Xu References: <20230131083257.3302830-1-usama.anjum@collabora.com> <20230131083257.3302830-2-usama.anjum@collabora.com> From: Muhammad Usama Anjum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A2C7B160002 X-Rspam-User: X-Stat-Signature: fx4crdh8nw79swxdtce7axoqih4e5541 X-HE-Tag: 1675332948-884742 X-HE-Meta: U2FsdGVkX19xS+qPakpfarJz7oIIU/uOM8x0c0i6CJg69ZlOK8MeDP4mOuZM2Hqc8SQhAcRVL3kE1zNKebaHL5jduUl/+1NgOoxPamxzBwxAXkeQ4sqGBOBZG3lxdGlOcLsP9RG81P88kMVh0cUAena8JIhI1cpE2ytHrOsBBz/pQhFm3fJFUGlm4bsUDhP+ohvr8J8eYddGscGcLYLlkWCJi02y1PrSyv8xt45UkkhcL5KLRJZ5EegV7ptexAwJgDFZI9AkxjeL1wNFciC9DZdjDwqSV5fpkezh6d/VxyFibVN1te6NPbwctEoPwA39N10kjfs/trGKgzZYVAJyn4Z6j/V58Ide3L0kJDTOFs7MLukaoYmkDfiTfo/rAqZ5MhxqtfOE7PDltcCaEJ+K6RhT13WJadeC7awIRajuyNw1K4IiDkOk57aRFBWpHv9SxX59DSkVdeCpd7eLpmrhZuaNlSDb9y9go2WaSTRjzArcgmOJ2c2TlcwhnYpfwGXg/v6VPl/WS7oxzoZIAK0yzQX4WRS1DonAyBHLGwZnoMPPE2WK3qZ9vbp7XotrRGkZRdF2sh+fOB4QXq8ceiX0T1FG7h9JK4dSsBpgUw7BhnR4ZMkQi5VPQlxGo5NPPrnCwD04E3w6fwWbkwcJ2NIxbpMictLN0Nnl0zohgGGA0T5cOenLQTQelbdcvro31kqaNEvYv0UBfSEnXiUKVmpqpsr6jIX7OTbzHcBiJXHvtlvpWEvYRrkvL1iOd5j17FT75828UBf9GX+JTlCyKIVr0jFKDh7NPPtIuRtKCigfltdKIMxiwkhVW2J5kJpMzBbbb/9E8zbWblQYFvTvPob5IR4HAdDv6AUnRIVeSymKaL786tyRSm4U/WIe/RsUq6gNsxPUfB+z29oYR7qALpr3s4vLIxIj2rHFclZs0MWZ9sMFH1Mmzu25QzMv8Uf3LRYuaGy3ammjPDFE+jaaVZD PWTRQO6M FKMGoaXkKwyZxh0RQSYPRABD3/R863Gyw2pFmqW3KTk/699azIjmLR1t2FiVWE6YqlgYgt+p+Jmem284IYDwJwOqJbXwTiPn/gHH++766F9AmJOg3PL5I0mv9BGMHXS5YYG594G+nevJSl88jHOnLZA8ZQ+IrdbrGHzASBd6rupvufA510YbIoZQ6WFj+pvD9M/gICjXah4eUXrRnF1Hwg0r2tNGFFunt2JZvOfA5SUHtI2MZqXOEgCffS+emUoltSNUng6jsJccD3Az6ps7Tw0Twsha09KBE+y6Bf2no5r+c7Fo= 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: Hi, Thank you so much for reviewing. On 2/2/23 3:51 AM, Peter Xu wrote: > On Tue, Jan 31, 2023 at 01:32:55PM +0500, Muhammad Usama Anjum wrote: >> Add new WP Async mode (UFFD_FEATURE_WP_ASYNC) which resolves the page >> faults on its own. It can be used to track that which pages have been >> written-to from the time the pages were write-protected. It is very >> efficient way to track the changes as uffd is by nature pte/pmd based. >> >> UFFD synchronous WP sends the page faults to the userspace where the >> pages which have been written-to can be tracked. But it is not efficient. >> This is why this asynchronous version is being added. After setting the >> WP Async, the pages which have been written to can be found in the pagemap >> file or information can be obtained from the PAGEMAP_IOCTL. >> >> Suggested-by: Peter Xu >> Signed-off-by: Muhammad Usama Anjum >> --- >> Changes in v9: >> - Correct the fault resolution with code contributed by Peter >> >> Changes in v7: >> - Remove UFFDIO_WRITEPROTECT_MODE_ASYNC_WP and add UFFD_FEATURE_WP_ASYNC >> - Handle automatic page fault resolution in better way (thanks to Peter) >> >> update to wp async >> --- >> fs/userfaultfd.c | 11 +++++++++++ >> include/linux/userfaultfd_k.h | 6 ++++++ >> include/uapi/linux/userfaultfd.h | 8 +++++++- >> mm/memory.c | 23 ++++++++++++++++++++--- >> 4 files changed, 44 insertions(+), 4 deletions(-) >> >> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c >> index 15a5bf765d43..c17835a0e842 100644 >> --- a/fs/userfaultfd.c >> +++ b/fs/userfaultfd.c >> @@ -1867,6 +1867,10 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx, >> mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP; >> mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE; >> >> + /* The unprotection is not supported if in async WP mode */ >> + if (!mode_wp && (ctx->features & UFFD_FEATURE_WP_ASYNC)) >> + return -EINVAL; >> + >> if (mode_wp && mode_dontwake) >> return -EINVAL; >> >> @@ -1950,6 +1954,13 @@ static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg) >> return ret; >> } >> >> +int userfaultfd_wp_async(struct vm_area_struct *vma) >> +{ >> + struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx; >> + >> + return (ctx && (ctx->features & UFFD_FEATURE_WP_ASYNC)); >> +} >> + >> static inline unsigned int uffd_ctx_features(__u64 user_features) >> { >> /* >> diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h >> index 9df0b9a762cc..94dcb4dc1b4a 100644 >> --- a/include/linux/userfaultfd_k.h >> +++ b/include/linux/userfaultfd_k.h >> @@ -179,6 +179,7 @@ extern int userfaultfd_unmap_prep(struct mm_struct *mm, unsigned long start, >> unsigned long end, struct list_head *uf); >> extern void userfaultfd_unmap_complete(struct mm_struct *mm, >> struct list_head *uf); >> +extern int userfaultfd_wp_async(struct vm_area_struct *vma); >> >> #else /* CONFIG_USERFAULTFD */ >> >> @@ -274,6 +275,11 @@ static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) >> return false; >> } >> >> +static inline int userfaultfd_wp_async(struct vm_area_struct *vma) >> +{ >> + return false; >> +} >> + >> #endif /* CONFIG_USERFAULTFD */ >> >> static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry) >> diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h >> index 005e5e306266..f4252ef40071 100644 >> --- a/include/uapi/linux/userfaultfd.h >> +++ b/include/uapi/linux/userfaultfd.h >> @@ -38,7 +38,8 @@ >> UFFD_FEATURE_MINOR_HUGETLBFS | \ >> UFFD_FEATURE_MINOR_SHMEM | \ >> UFFD_FEATURE_EXACT_ADDRESS | \ >> - UFFD_FEATURE_WP_HUGETLBFS_SHMEM) >> + UFFD_FEATURE_WP_HUGETLBFS_SHMEM | \ >> + UFFD_FEATURE_WP_ASYNC) >> #define UFFD_API_IOCTLS \ >> ((__u64)1 << _UFFDIO_REGISTER | \ >> (__u64)1 << _UFFDIO_UNREGISTER | \ >> @@ -203,6 +204,10 @@ struct uffdio_api { >> * >> * UFFD_FEATURE_WP_HUGETLBFS_SHMEM indicates that userfaultfd >> * write-protection mode is supported on both shmem and hugetlbfs. >> + * >> + * UFFD_FEATURE_WP_ASYNC indicates that userfaultfd write-protection >> + * asynchronous mode is supported in which the write fault is automatically >> + * resolved and write-protection is un-set. > > Please mention a few other things: > > - It only supports anon and shmem (so hugetlb is not supported) > > - It will only take effect when any vma is registered with wr-protection > mode. Otherwise the flag will be ignored. > > In userfaultfd_register(), we need to fail the ioctl if anyone tries to > register any hugetlb vma with this new flag set. Added. Thanks > >> */ >> #define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0) >> #define UFFD_FEATURE_EVENT_FORK (1<<1) >> @@ -217,6 +222,7 @@ struct uffdio_api { >> #define UFFD_FEATURE_MINOR_SHMEM (1<<10) >> #define UFFD_FEATURE_EXACT_ADDRESS (1<<11) >> #define UFFD_FEATURE_WP_HUGETLBFS_SHMEM (1<<12) >> +#define UFFD_FEATURE_WP_ASYNC (1<<13) >> __u64 features; >> >> __u64 ioctls; >> diff --git a/mm/memory.c b/mm/memory.c >> index 4000e9f017e0..04843e35550e 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -3351,8 +3351,21 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) >> >> if (likely(!unshare)) { >> if (userfaultfd_pte_wp(vma, *vmf->pte)) { >> - pte_unmap_unlock(vmf->pte, vmf->ptl); >> - return handle_userfault(vmf, VM_UFFD_WP); >> + if (userfaultfd_wp_async(vma)) { >> + /* >> + * Nothing needed (cache flush, TLB invalidations, >> + * etc.) because we're only removing the uffd-wp bit, >> + * which is completely invisible to the user. >> + */ >> + pte_t pte = pte_clear_uffd_wp(*vmf->pte); >> + >> + set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte); >> + /* Update this to be prepared for following up CoW handling */ >> + vmf->orig_pte = pte; >> + } else { >> + pte_unmap_unlock(vmf->pte, vmf->ptl); >> + return handle_userfault(vmf, VM_UFFD_WP); >> + } >> } >> >> /* >> @@ -4812,8 +4825,11 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf) >> >> if (vma_is_anonymous(vmf->vma)) { >> if (likely(!unshare) && >> - userfaultfd_huge_pmd_wp(vmf->vma, vmf->orig_pmd)) >> + userfaultfd_huge_pmd_wp(vmf->vma, vmf->orig_pmd)) { >> + if (userfaultfd_wp_async(vmf->vma)) >> + goto split_and_return; >> return handle_userfault(vmf, VM_UFFD_WP); >> + } >> return do_huge_pmd_wp_page(vmf); >> } >> >> @@ -4825,6 +4841,7 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf) >> } >> } >> >> +split_and_return: > > The "and_return" is superfluous, IMHO. Just make it "split"? > >> /* COW or write-notify handled on pte level: split pmd. */ >> __split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL); > > Would you also update Documentation/admin-guide/mm/userfaultfd.rst in the > same patch? Okay. I'll add some documentation. > > Thanks, > -- BR, Muhammad Usama Anjum