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Fri, 21 Feb 2025 12:05:29 +0000 Received: from BYAPR10MB3366.namprd10.prod.outlook.com ([fe80::baf2:dff1:d471:1c9]) by BYAPR10MB3366.namprd10.prod.outlook.com ([fe80::baf2:dff1:d471:1c9%5]) with mapi id 15.20.8466.015; Fri, 21 Feb 2025 12:05:29 +0000 From: Lorenzo Stoakes To: Andrew Morton Cc: Jonathan Corbet , Shuah Khan , David Hildenbrand , Suren Baghdasaryan , Kalesh Singh , "Liam R . Howlett" , Matthew Wilcox , Vlastimil Babka , "Paul E . McKenney" , Jann Horn , Juan Yescas , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-api@vger.kernel.org Subject: [PATCH 1/2] fs/proc/task_mmu: add guard region bit to pagemap Date: Fri, 21 Feb 2025 12:05:22 +0000 Message-ID: <521d99c08b975fb06a1e7201e971cc24d68196d1.1740139449.git.lorenzo.stoakes@oracle.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: References: X-ClientProxiedBy: LO2P265CA0427.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:a0::31) To BYAPR10MB3366.namprd10.prod.outlook.com (2603:10b6:a03:14f::25) Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR10MB3366:EE_|LV8PR10MB7822:EE_ X-MS-Office365-Filtering-Correlation-Id: 234fd4f1-03d7-435e-04a2-08dd52700900 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024; 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This is intentional, as to provide this information in VMA metadata would contradict the intent of the feature (providing a means to change fault behaviour at a page table level rather than a VMA level), and would require VMA metadata operations to scan page tables, which is unacceptable. In many cases, users have no need to reflect and determine what regions have been designated guard regions, as it is the user who has established them in the first place. But in some instances, such as monitoring software, or software that relies upon being able to ascertain the nature of mappings within a remote process for instance, it becomes useful to be able to determine which pages have the guard region marker applied. This patch makes use of an unused pagemap bit (58) to provide this information. This patch updates the documentation at the same time as making the change such that the implementation of the feature and the documentation of it are tied together. Signed-off-by: Lorenzo Stoakes --- Documentation/admin-guide/mm/pagemap.rst | 3 ++- fs/proc/task_mmu.c | 6 +++++- 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index caba0f52dd36..a297e824f990 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -21,7 +21,8 @@ There are four components to pagemap: * Bit 56 page exclusively mapped (since 4.2) * Bit 57 pte is uffd-wp write-protected (since 5.13) (see Documentation/admin-guide/mm/userfaultfd.rst) - * Bits 58-60 zero + * Bit 58 pte is a guard region (since 6.15) (see madvise (2) man page) + * Bits 59-60 zero * Bit 61 page is file-page or shared-anon (since 3.5) * Bit 62 page swapped * Bit 63 page present diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index f02cd362309a..c17615e21a5d 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1632,6 +1632,7 @@ struct pagemapread { #define PM_SOFT_DIRTY BIT_ULL(55) #define PM_MMAP_EXCLUSIVE BIT_ULL(56) #define PM_UFFD_WP BIT_ULL(57) +#define PM_GUARD_REGION BIT_ULL(58) #define PM_FILE BIT_ULL(61) #define PM_SWAP BIT_ULL(62) #define PM_PRESENT BIT_ULL(63) @@ -1732,6 +1733,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm, page = pfn_swap_entry_to_page(entry); if (pte_marker_entry_uffd_wp(entry)) flags |= PM_UFFD_WP; + if (is_guard_swp_entry(entry)) + flags |= PM_GUARD_REGION; } if (page) { @@ -1931,7 +1934,8 @@ static const struct mm_walk_ops pagemap_ops = { * Bit 55 pte is soft-dirty (see Documentation/admin-guide/mm/soft-dirty.rst) * Bit 56 page exclusively mapped * Bit 57 pte is uffd-wp write-protected - * Bits 58-60 zero + * Bit 58 pte is a guard region + * Bits 59-60 zero * Bit 61 page is file-page or shared-anon * Bit 62 page swapped * Bit 63 page present From patchwork Fri Feb 21 12:05:23 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lorenzo Stoakes X-Patchwork-Id: 13985319 Received: from mx0a-00069f02.pphosted.com (mx0a-00069f02.pphosted.com [205.220.165.32]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9837A2101A0; Fri, 21 Feb 2025 12:05:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; 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McKenney" , Jann Horn , Juan Yescas , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-api@vger.kernel.org Subject: [PATCH 2/2] tools/selftests: add guard region test for /proc/$pid/pagemap Date: Fri, 21 Feb 2025 12:05:23 +0000 Message-ID: <164feb0a43ae72650e6b20c3910213f469566311.1740139449.git.lorenzo.stoakes@oracle.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: References: X-ClientProxiedBy: LNXP123CA0011.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:d2::23) To BYAPR10MB3366.namprd10.prod.outlook.com (2603:10b6:a03:14f::25) Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR10MB3366:EE_|LV8PR10MB7822:EE_ X-MS-Office365-Filtering-Correlation-Id: 19f0b30e-b1b7-41a7-7c84-08dd52700ac3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024; 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As a part of this change, update vm_util.h to add the new bit (note there is no header file in the kernel where this is exposed, the user is expected to provide their own mask) and utilise the helper functions there for pagemap functionality. Signed-off-by: Lorenzo Stoakes Signed-off-by: Lorenzo Stoakes Reviewed-by: Kalesh Singh --- tools/testing/selftests/mm/guard-regions.c | 47 ++++++++++++++++++++++ tools/testing/selftests/mm/vm_util.h | 1 + 2 files changed, 48 insertions(+) diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c index ea9b5815e828..0c7183e8b661 100644 --- a/tools/testing/selftests/mm/guard-regions.c +++ b/tools/testing/selftests/mm/guard-regions.c @@ -19,6 +19,7 @@ #include #include #include +#include "vm_util.h" /* * Ignore the checkpatch warning, as per the C99 standard, section 7.14.1.1: @@ -2032,4 +2033,50 @@ TEST_F(guard_regions, anon_zeropage) ASSERT_EQ(munmap(ptr, 10 * page_size), 0); } +/* + * Assert that /proc/$pid/pagemap correctly identifies guard region ranges. + */ +TEST_F(guard_regions, pagemap) +{ + const unsigned long page_size = self->page_size; + int proc_fd; + char *ptr; + int i; + + proc_fd = open("/proc/self/pagemap", O_RDONLY); + ASSERT_NE(proc_fd, -1); + + ptr = mmap_(self, variant, NULL, 10 * page_size, + PROT_READ | PROT_WRITE, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Read from pagemap, and assert no guard regions are detected. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + unsigned long entry = pagemap_get_entry(proc_fd, ptr_p); + unsigned long masked = entry & PM_GUARD_REGION_MASK; + + ASSERT_EQ(masked, 0); + } + + /* Install a guard region in every other page. */ + for (i = 0; i < 10; i += 2) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(madvise(ptr_p, page_size, MADV_GUARD_INSTALL), 0); + } + + /* Re-read from pagemap, and assert guard regions are detected. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + unsigned long entry = pagemap_get_entry(proc_fd, ptr_p); + unsigned long masked = entry & PM_GUARD_REGION_MASK; + + ASSERT_EQ(masked, i % 2 == 0 ? PM_GUARD_REGION_MASK : 0); + } + + ASSERT_EQ(close(proc_fd), 0); + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h index b60ac68a9dc8..73a11443b7f6 100644 --- a/tools/testing/selftests/mm/vm_util.h +++ b/tools/testing/selftests/mm/vm_util.h @@ -10,6 +10,7 @@ #define PM_SOFT_DIRTY BIT_ULL(55) #define PM_MMAP_EXCLUSIVE BIT_ULL(56) #define PM_UFFD_WP BIT_ULL(57) +#define PM_GUARD_REGION_MASK BIT_ULL(58) #define PM_FILE BIT_ULL(61) #define PM_SWAP BIT_ULL(62) #define PM_PRESENT BIT_ULL(63)