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charset=UTF-8 References: <20261013093600.54995-1-zhaogongyi@bytedance.com> <6a10b61f-5c4f-4d04-9742-97a358147c39@arm.com> To: "Dev Jain" , , Subject: Re: [PATCH] arm64/mm: restrict transparent contpte mappings to valid PTEs Content-Transfer-Encoding: 7bit Date: Wed, 14 Oct 2026 14:16:33 +0800 Mime-Version: 1.0 X-Lms-Return-Path: In-Reply-To: <6a10b61f-5c4f-4d04-9742-97a358147c39@arm.com> X-Stat-Signature: 7e5cwn7kh8fxy576drs3664p7u8zqgiz X-Rspamd-Queue-Id: 8F167100004 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1791958628-453207 X-HE-Meta: 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 CfYRfE5y 6zhleM1oTEFqENzZu84xv1wPTDCwZhuCxiRX4L/rqb2xi3oZ3KR/RBImjAD8Pxk5ouWbYYtIwvn5t3qhoP8RJDii7Kkn/BK+xIFpO3Suf+Ov5J8teIb0bVv8Lf4J3uRwDUASs15tFH8HsNU5ypUc1JhsYvL4X2XJL0yO+40b6neJdYZSnf2TflC1qs10Y/n4hzdLAYUC08mqzBvfHSrRS80lFHyD3iCLage+/Hw6vkYsAW12FHyDuZ+NosTr1VNus1niYWIJa8tl3FQHx5ltxwQFc/Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/10/13 18:13, Dev Jain wrote: > > > Thanks, could you please give the code of the reproducer. That will > save us some time. > > Hi Dev, Sure, sorry for not including it in the first mail. The standalone reproducer I used is below. It assumes an arm64 kernel with CONFIG_ARM64_CONTPTE=y and a CONT_PTE_SIZE anonymous mTHP order available. When run as root, it tries to enable THP and the matching mTHP order through sysfs. These sysfs writes are best-effort; if the matching order is not available or cannot be enabled, the reproducer may not hit the issue. On a 4K-page kernel, CONT_PTE_SIZE is 64KB. Compile and run: gcc -O2 -Wall contpte_guard_repro.c -o contpte_guard_repro ./contpte_guard_repro 100 On my unfixed KASAN kernel with panic_on_warn=1, the first iteration hit the bad swap entry / swap_put_entries_direct() warning. With this patch, 100 iterations completed without warnings. Here is the reproducer: #define _GNU_SOURCE #include #include #include #include #include #include #include #ifndef MADV_HUGEPAGE #define MADV_HUGEPAGE 14 #endif #ifndef MADV_POPULATE_WRITE #define MADV_POPULATE_WRITE 23 #endif #ifndef MADV_GUARD_INSTALL #define MADV_GUARD_INSTALL 102 #endif #ifndef MADV_GUARD_REMOVE #define MADV_GUARD_REMOVE 103 #endif static void write_file(const char *path, const char *val) { int fd = open(path, O_WRONLY | O_CLOEXEC); if (fd < 0) return; (void)write(fd, val, strlen(val)); close(fd); } static void write_clear_refs(void) { int fd = open("/proc/self/clear_refs", O_WRONLY | O_CLOEXEC); if (fd < 0) { perror("open clear_refs"); exit(1); } if (write(fd, "1", 1) != 1) { perror("write clear_refs"); exit(1); } close(fd); } static unsigned long contpte_size(unsigned long page_size) { if (page_size == 4096) return 64 * 1024; if (page_size == 16384 || page_size == 65536) return 2 * 1024 * 1024; fprintf(stderr, "unsupported page size %lu\n", page_size); exit(1); } static void enable_mthp(unsigned long size) { char path[256]; write_file("/sys/kernel/mm/transparent_hugepage/enabled", "always\n"); write_file("/sys/kernel/mm/transparent_hugepage/defrag", "always\n"); snprintf(path, sizeof(path), "/sys/kernel/mm/transparent_hugepage/hugepages-%lukB/enabled", size / 1024); write_file(path, "always\n"); } static void touch_range(char *p, unsigned long len, unsigned long page_size) { for (unsigned long off = 0; off < len; off += page_size) p[off] = (char)off; } int main(int argc, char **argv) { const int loops = argc > 1 ? atoi(argv[1]) : 1; const unsigned long page_size = sysconf(_SC_PAGESIZE); const unsigned long csize = contpte_size(page_size); const unsigned long nr_pages = 2 * csize / page_size; const unsigned long len = nr_pages * page_size; const unsigned long map_len = len + csize; const unsigned long guard_idx = csize / page_size - 3; enable_mthp(csize); for (int i = 0; i < loops; i++) { char *map, *p; map = mmap(NULL, map_len, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (map == MAP_FAILED) { perror("mmap"); return 1; } p = (char *)(((unsigned long)map + csize - 1) & ~(csize - 1)); if (madvise(p, len, MADV_HUGEPAGE)) perror("madvise MADV_HUGEPAGE"); if (madvise(p, len, MADV_POPULATE_WRITE)) perror("madvise MADV_POPULATE_WRITE"); touch_range(p, len, page_size); if (mprotect(p, len, PROT_NONE)) { perror("mprotect PROT_NONE"); return 1; } if (madvise(p + guard_idx * page_size, page_size, MADV_GUARD_INSTALL)) { perror("madvise MADV_GUARD_INSTALL"); return 1; } write_clear_refs(); if (munmap(map, map_len)) { perror("munmap"); return 1; } } return 0; } Thanks, Zhao