Received: by 2002:a05:6a10:8c0a:0:0:0:0 with SMTP id go10csp138074pxb; Fri, 15 Jan 2021 09:16:12 -0800 (PST) X-Google-Smtp-Source: ABdhPJx7uYe9aPHFXiQWVS7MTVeyVfN8qIFTL8aSKAHzoKmM9DCnh9PltIWtXsFTDRXQzHKC8Hqd X-Received: by 2002:a17:906:2648:: with SMTP id i8mr4198224ejc.262.1610730972321; Fri, 15 Jan 2021 09:16:12 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1610730972; cv=none; d=google.com; s=arc-20160816; b=xr7o1VTLJErL5p+tG/B2/5skyTpJrwHHRO3b3hgsXjk5EssijWoAmjyg4vNkAuA1vG iwSMWit1LznduQoxGheZWgZtXRkhpcsLXyU7DN0YrOlSX4zOGPozaRjGB+vVi9DLDrWQ GDUeXG9yO1elfjubutsZFcEWMO3jVpWGbEZKexdMhGxnYKpPjtwrwesjADsfIBzSmmk7 ZlCfVtrwh1PZjXMaUQBc3Asdpwx1JkBi51lHbofDi/bQCaTVRZiXhFgrPArwnfP9UDTq eNoxf9S7w+RpH4RcUUucXubweRMccfQaMXyFQd4t261DoOaedv8/+3gFs8ATbqWVMwHh TJRA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature; bh=a5KLb2lATkQ/XNiv9F7KPoJriimXjMJy8UfLukuBk5Y=; b=gyQvzqFNBUTFgcgsS/02Uyig1tWCdlk9g7qziIlO+sVSGIbT57ceFaAMbf5eBW/T3M 1puk5BCIMaARxpNqPTcfAtPPYPRgs+iifEiVNqWFWwBm7zxjEtDVo+bMc3KlWwiRjucE svQhlsbaPxk8Gx90N3boNvMLS9PUShGlGbKXYBqKHHeRH9PCJUu+S4NoYMMk/3fn7uOc TqCXPpjgjuVyZfw/LBOmu1dmjW//6bwwPS+5TKniZZbW4SSG3PS6uaOxJYnxedPWAUnk C/uMio+i+t8kILmfmDJ/PPoZdQizOS+ZevLaUq/XUIiRAa++0W0miAXze/aHG6cIHG0R CDpQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=ByAyTtr4; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id qq23si4065455ejb.232.2021.01.15.09.15.47; Fri, 15 Jan 2021 09:16:12 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=ByAyTtr4; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728649AbhAORNg (ORCPT + 99 others); Fri, 15 Jan 2021 12:13:36 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26404 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728818AbhAORNf (ORCPT ); Fri, 15 Jan 2021 12:13:35 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610730727; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=a5KLb2lATkQ/XNiv9F7KPoJriimXjMJy8UfLukuBk5Y=; b=ByAyTtr4FaXoTSEM7NMgrS/2pV6NGqhNTHVnOix3ys46fvdUL61O5V4sfXy6YERBwIjvxs 9qu99MP+n1b2kizALmqPYPm9M+izbE5Tp0N8i9kVD+fqKU3Q9M/R8yAJ1PrcsDeq9X1BoE k3qvN13e3mUVJ0+R2SEWaNkigzYm7GE= Received: from mail-qk1-f198.google.com (mail-qk1-f198.google.com [209.85.222.198]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-10-15TJhtwPP7iAPw6hWIQefA-1; Fri, 15 Jan 2021 12:09:37 -0500 X-MC-Unique: 15TJhtwPP7iAPw6hWIQefA-1 Received: by mail-qk1-f198.google.com with SMTP id f27so8614470qkh.0 for ; Fri, 15 Jan 2021 09:09:37 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=a5KLb2lATkQ/XNiv9F7KPoJriimXjMJy8UfLukuBk5Y=; b=qa0DB7SU48puxLoZ0KViVJoWafEKwb30p1rbHQBpYogjxlGID8z3SpHcPbnzp0v+YV ftbufbFN+Nnoxe1UDsQP9wvyKCtTh+2kzmdnD9WWaTOwDrwlr4GWc8UzdtAc92Fbj5RI MgMuuae16+JPMPKtrcDlRZmmshPvJrOeXAurRom9Hapyvc87yaHwDVtguifEKuLS1oY1 rA40fFeXvFAmB/tOyN8VgRP/OEz6m3ApJTCFjKQVtnPw13n+E+9hou/3PkYKzjaxzDDw v40QkGQ+NCUwRlfMn/F0+kOXhq2WxbiCM3XcBIn0F/eKaWdvxlxYVEGy33NLigvFpzk1 EG1A== X-Gm-Message-State: AOAM531kO9J0Fe5sWqjuKpH1Ndwo1SwZWClBoLa7DKSOTTG12Ijvuenk LaiNVeeZ14jceFXW32266f+lDVE6I15wCtpK3Pa1hw8rNqEvD3N69QMDCtb7d8o2AlFsKYgFEqQ rsRM5qDp3CXUyEG1M0+ZoQRZ5CSiV5pMXx/YzoAQT757j4wGXoMtmYEX0xRFxW+fSCKTFxjNc8A == X-Received: by 2002:ac8:396d:: with SMTP id t42mr12482442qtb.273.1610730576025; Fri, 15 Jan 2021 09:09:36 -0800 (PST) X-Received: by 2002:ac8:396d:: with SMTP id t42mr12482366qtb.273.1610730575395; Fri, 15 Jan 2021 09:09:35 -0800 (PST) Received: from localhost.localdomain ([142.126.83.202]) by smtp.gmail.com with ESMTPSA id d123sm5187840qke.95.2021.01.15.09.09.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 Jan 2021 09:09:34 -0800 (PST) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Mike Rapoport , Mike Kravetz , peterx@redhat.com, Jerome Glisse , "Kirill A . Shutemov" , Hugh Dickins , Axel Rasmussen , Matthew Wilcox , Andrew Morton , Andrea Arcangeli , Nadav Amit Subject: [PATCH RFC 13/30] shmem/userfaultfd: Persist uffd-wp bit across zapping for file-backed Date: Fri, 15 Jan 2021 12:08:50 -0500 Message-Id: <20210115170907.24498-14-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210115170907.24498-1-peterx@redhat.com> References: <20210115170907.24498-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org File-backed memory is prone to being unmapped at any time. It means all information in the pte will be dropped, including the uffd-wp flag. Since the uffd-wp info cannot be stored in page cache or swap cache, persist this wr-protect information by installing the special uffd-wp marker pte when we're going to unmap a uffd wr-protected pte. When the pte is accessed again, we will know it's previously wr-protected by recognizing the special pte. Meanwhile add a new flag ZAP_FLAG_DROP_FILE_UFFD_WP when we don't want to persist such an information. For example, when destroying the whole vma, or punching a hole in a shmem file. For the latter, we can only drop the uffd-wp bit when holding the page lock. It means the unmap_mapping_range() in shmem_fallocate() still reuqires to zap without ZAP_FLAG_DROP_FILE_UFFD_WP because that's still racy with the page faults. Signed-off-by: Peter Xu --- include/linux/mm.h | 11 ++++++++++ include/linux/mm_inline.h | 43 +++++++++++++++++++++++++++++++++++++++ mm/memory.c | 42 +++++++++++++++++++++++++++++++++++++- mm/rmap.c | 8 ++++++++ mm/truncate.c | 8 +++++++- 5 files changed, 110 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 57bb3d680844..e4aba745be62 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1634,6 +1634,8 @@ extern void user_shm_unlock(size_t, struct user_struct *); #define ZAP_FLAG_CHECK_MAPPING BIT(0) /* Whether to skip zapping swap entries */ #define ZAP_FLAG_SKIP_SWAP BIT(1) +/* Whether to completely drop uffd-wp entries for file-backed memory */ +#define ZAP_FLAG_DROP_FILE_UFFD_WP BIT(2) /* * Parameter block passed down to zap_pte_range in exceptional cases. @@ -1666,6 +1668,15 @@ zap_skip_swap(struct zap_details *details) return details->zap_flags & ZAP_FLAG_SKIP_SWAP; } +static inline bool +zap_drop_file_uffd_wp(struct zap_details *details) +{ + if (!details) + return false; + + return details->zap_flags & ZAP_FLAG_DROP_FILE_UFFD_WP; +} + struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_t pte); struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index 8fc71e9d7bb0..da4c710859e6 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -4,6 +4,8 @@ #include #include +#include +#include /** * page_is_file_lru - should the page be on a file LRU or anon LRU? @@ -125,4 +127,45 @@ static __always_inline enum lru_list page_lru(struct page *page) } return lru; } + +/* + * If this pte is wr-protected by uffd-wp in any form, arm the special pte to + * replace a none pte. NOTE! This should only be called when *pte is already + * cleared so we will never accidentally replace something valuable. Meanwhile + * none pte also means we are not demoting the pte so if tlb flushed then we + * don't need to do it again; otherwise if tlb flush is postponed then it's + * even better. + * + * Must be called with pgtable lock held. + */ +static inline void +pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr, + pte_t *pte, pte_t pteval) +{ +#ifdef CONFIG_USERFAULTFD + bool arm_uffd_pte = false; + + /* The current status of the pte should be "cleared" before calling */ + WARN_ON_ONCE(!pte_none(*pte)); + + if (vma_is_anonymous(vma)) + return; + + /* A uffd-wp wr-protected normal pte */ + if (unlikely(pte_present(pteval) && pte_uffd_wp(pteval))) + arm_uffd_pte = true; + + /* + * A uffd-wp wr-protected swap pte. Note: this should even work for + * pte_swp_uffd_wp_special() too. + */ + if (unlikely(is_swap_pte(pteval) && pte_swp_uffd_wp(pteval))) + arm_uffd_pte = true; + + if (unlikely(arm_uffd_pte)) + set_pte_at(vma->vm_mm, addr, pte, + pte_swp_mkuffd_wp_special(vma)); +#endif +} + #endif diff --git a/mm/memory.c b/mm/memory.c index afe09fccdee1..f87b5a8a098e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -73,6 +73,7 @@ #include #include #include +#include #include @@ -1194,6 +1195,21 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) return ret; } +/* + * This function makes sure that we'll replace the none pte with an uffd-wp + * swap special pte marker when necessary. Must be with the pgtable lock held. + */ +static inline void +zap_install_uffd_wp_if_needed(struct vm_area_struct *vma, + unsigned long addr, pte_t *pte, + struct zap_details *details, pte_t pteval) +{ + if (zap_drop_file_uffd_wp(details)) + return; + + pte_install_uffd_wp_if_needed(vma, addr, pte, pteval); +} + static unsigned long zap_pte_range(struct mmu_gather *tlb, struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr, unsigned long end, @@ -1231,6 +1247,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm); tlb_remove_tlb_entry(tlb, pte, addr); + zap_install_uffd_wp_if_needed(vma, addr, pte, details, + ptent); if (unlikely(!page)) continue; @@ -1255,6 +1273,22 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, continue; } + /* + * If this is a special uffd-wp marker pte... Drop it only if + * enforced to do so. + */ + if (unlikely(is_swap_special_pte(ptent))) { + WARN_ON_ONCE(!pte_swp_uffd_wp_special(ptent)); + /* + * If this is a common unmap of ptes, keep this as is. + * Drop it only if this is a whole-vma destruction. + */ + if (zap_drop_file_uffd_wp(details)) + ptep_get_and_clear_full(mm, addr, pte, + tlb->fullmm); + continue; + } + entry = pte_to_swp_entry(ptent); if (is_device_private_entry(entry)) { struct page *page = device_private_entry_to_page(entry); @@ -1265,6 +1299,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, rss[mm_counter(page)]--; page_remove_rmap(page, false); put_page(page); + zap_install_uffd_wp_if_needed(vma, addr, pte, details, + ptent); continue; } @@ -1282,6 +1318,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, if (unlikely(!free_swap_and_cache(entry))) print_bad_pte(vma, addr, ptent, NULL); pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); + zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent); } while (pte++, addr += PAGE_SIZE, addr != end); add_mm_rss_vec(mm, rss); @@ -1481,12 +1518,15 @@ void unmap_vmas(struct mmu_gather *tlb, unsigned long end_addr) { struct mmu_notifier_range range; + struct zap_details details = { + .zap_flags = ZAP_FLAG_DROP_FILE_UFFD_WP, + }; mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm, start_addr, end_addr); mmu_notifier_invalidate_range_start(&range); for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) - unmap_single_vma(tlb, vma, start_addr, end_addr, NULL); + unmap_single_vma(tlb, vma, start_addr, end_addr, &details); mmu_notifier_invalidate_range_end(&range); } diff --git a/mm/rmap.c b/mm/rmap.c index 31b29321adfe..f6cc0b9b1963 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -72,6 +72,7 @@ #include #include #include +#include #include @@ -1560,6 +1561,13 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, pteval = ptep_clear_flush(vma, address, pvmw.pte); } + /* + * Now the pte is cleared. If this is uffd-wp armed pte, we + * may want to replace a none pte with a marker pte if it's + * file-backed, so we don't lose the tracking information. + */ + pte_install_uffd_wp_if_needed(vma, address, pvmw.pte, pteval); + /* Move the dirty bit to the page. Now the pte is gone. */ if (pte_dirty(pteval)) set_page_dirty(page); diff --git a/mm/truncate.c b/mm/truncate.c index dac66749e400..35df3b1d301e 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -179,7 +179,13 @@ truncate_cleanup_page(struct address_space *mapping, struct page *page) if (page_mapped(page)) { unsigned int nr = thp_nr_pages(page); unmap_mapping_pages(mapping, page->index, nr, - ZAP_FLAG_CHECK_MAPPING); + ZAP_FLAG_CHECK_MAPPING | + /* + * Now it's safe to drop uffd-wp because + * we're with page lock, and the page is + * being truncated. + */ + ZAP_FLAG_DROP_FILE_UFFD_WP); } if (page_has_private(page)) -- 2.26.2