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17 Nov 2022 06:34:16 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10534"; a="814534057" X-IronPort-AV: E=Sophos;i="5.96,171,1665471600"; d="scan'208";a="814534057" Received: from vrgatne-mobl4.amr.corp.intel.com (HELO [10.209.115.197]) ([10.209.115.197]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Nov 2022 06:34:15 -0800 Content-Type: multipart/mixed; boundary="------------5Ob6KInVGuG0YbX9A7MUQQSR" Message-ID: <4208866d-338f-4781-7ff9-023f016c5b07@intel.com> Date: Thu, 17 Nov 2022 06:34:15 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: WARNING: CPU: 0 PID: 0 at arch/x86/include/asm/kfence.h:46 kfence_protect Content-Language: en-US To: Marco Elver , Naresh Kamboju , Peter Zijlstra Cc: kasan-dev , X86 ML , open list , linux-mm , regressions@lists.linux.dev, lkft-triage@lists.linaro.org, Andrew Morton , Alexander Potapenko References: From: Dave Hansen In-Reply-To: ARC-Seal: i=1; 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dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=KMmprkMG; dmarc=pass (policy=none) header.from=intel.com; spf=pass (imf07.hostedemail.com: domain of dave.hansen@intel.com designates 134.134.136.31 as permitted sender) smtp.mailfrom=dave.hansen@intel.com X-Stat-Signature: siqr6w7o3x9sa7a8ur587noafbx7cryp X-HE-Tag: 1668695665-982877 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: This is a multi-part message in MIME format. --------------5Ob6KInVGuG0YbX9A7MUQQSR Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/17/22 05:58, Marco Elver wrote: > [ 0.663761] WARNING: CPU: 0 PID: 0 at arch/x86/include/asm/kfence.h:46 kfence_protect+0x7b/0x120 > [ 0.664033] WARNING: CPU: 0 PID: 0 at mm/kfence/core.c:234 kfence_protect+0x7d/0x120 > [ 0.664465] kfence: kfence_init failed Any chance you could add some debugging and figure out what actually made kfence call over? Was it the pte or the level? if (WARN_ON(!pte || level != PG_LEVEL_4K)) return false; I can see how the thing you bisected to might lead to a page table not being split, which could mess with the 'level' check. Also, is there a reason this code is mucking with the page tables directly? It seems, uh, rather wonky. This, for instance: > if (protect) > set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT)); > else > set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT)); > > /* > * Flush this CPU's TLB, assuming whoever did the allocation/free is > * likely to continue running on this CPU. > */ > preempt_disable(); > flush_tlb_one_kernel(addr); > preempt_enable(); Seems rather broken. I assume the preempt_disable() is there to get rid of some warnings. But, there is nothing I can see to *keep* the CPU that did the free from being different from the one where the TLB flush is performed until the preempt_disable(). That makes the flush_tlb_one_kernel() mostly useless. Is there a reason this code isn't using the existing page table manipulation functions and tries to code its own? What prevents it from using something like the attached patch? --------------5Ob6KInVGuG0YbX9A7MUQQSR Content-Type: text/x-patch; charset=UTF-8; name="kfence.patch" Content-Disposition: attachment; filename="kfence.patch" Content-Transfer-Encoding: base64 ZGlmZiAtLWdpdCBhL2FyY2gveDg2L2luY2x1ZGUvYXNtL2tmZW5jZS5oIGIvYXJjaC94ODYv aW5jbHVkZS9hc20va2ZlbmNlLmgKaW5kZXggZmY1YzcxMzRhMzdhLi41Y2RiM2ExZjM5OTUg MTAwNjQ0Ci0tLSBhL2FyY2gveDg2L2luY2x1ZGUvYXNtL2tmZW5jZS5oCisrKyBiL2FyY2gv eDg2L2luY2x1ZGUvYXNtL2tmZW5jZS5oCkBAIC0zNywzNCArMzcsMTMgQEAgc3RhdGljIGlu bGluZSBib29sIGFyY2hfa2ZlbmNlX2luaXRfcG9vbCh2b2lkKQogCXJldHVybiB0cnVlOwog fQogCi0vKiBQcm90ZWN0IHRoZSBnaXZlbiBwYWdlIGFuZCBmbHVzaCBUTEIuICovCiBzdGF0 aWMgaW5saW5lIGJvb2wga2ZlbmNlX3Byb3RlY3RfcGFnZSh1bnNpZ25lZCBsb25nIGFkZHIs IGJvb2wgcHJvdGVjdCkKIHsKLQl1bnNpZ25lZCBpbnQgbGV2ZWw7Ci0JcHRlX3QgKnB0ZSA9 IGxvb2t1cF9hZGRyZXNzKGFkZHIsICZsZXZlbCk7Ci0KLQlpZiAoV0FSTl9PTighcHRlIHx8 IGxldmVsICE9IFBHX0xFVkVMXzRLKSkKLQkJcmV0dXJuIGZhbHNlOwotCi0JLyoKLQkgKiBX ZSBuZWVkIHRvIGF2b2lkIElQSXMsIGFzIHdlIG1heSBnZXQgS0ZFTkNFIGFsbG9jYXRpb25z IG9yIGZhdWx0cwotCSAqIHdpdGggaW50ZXJydXB0cyBkaXNhYmxlZC4gVGhlcmVmb3JlLCB0 aGUgYmVsb3cgaXMgYmVzdC1lZmZvcnQsIGFuZAotCSAqIGRvZXMgbm90IGZsdXNoIFRMQnMg b24gYWxsIENQVXMuIFdlIGNhbiB0b2xlcmF0ZSBzb21lIGluYWNjdXJhY3k7Ci0JICogbGF6 eSBmYXVsdCBoYW5kbGluZyB0YWtlcyBjYXJlIG9mIGZhdWx0cyBhZnRlciB0aGUgcGFnZSBp cyBQUkVTRU5ULgotCSAqLwotCiAJaWYgKHByb3RlY3QpCi0JCXNldF9wdGUocHRlLCBfX3B0 ZShwdGVfdmFsKCpwdGUpICYgfl9QQUdFX1BSRVNFTlQpKTsKKwkJc2V0X21lbW9yeV9ucChh ZGRyLCBhZGRyICsgUEFHRV9TSVpFKTsKIAllbHNlCi0JCXNldF9wdGUocHRlLCBfX3B0ZShw dGVfdmFsKCpwdGUpIHwgX1BBR0VfUFJFU0VOVCkpOworCQlzZXRfbWVtb3J5X3AoYWRkciwg YWRkciArIFBBR0VfU0laRSk7CiAKLQkvKgotCSAqIEZsdXNoIHRoaXMgQ1BVJ3MgVExCLCBh c3N1bWluZyB3aG9ldmVyIGRpZCB0aGUgYWxsb2NhdGlvbi9mcmVlIGlzCi0JICogbGlrZWx5 IHRvIGNvbnRpbnVlIHJ1bm5pbmcgb24gdGhpcyBDUFUuCi0JICovCi0JcHJlZW1wdF9kaXNh YmxlKCk7Ci0JZmx1c2hfdGxiX29uZV9rZXJuZWwoYWRkcik7Ci0JcHJlZW1wdF9lbmFibGUo KTsKIAlyZXR1cm4gdHJ1ZTsKIH0KIAo= --------------5Ob6KInVGuG0YbX9A7MUQQSR--