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X-CSE-ConnectionGUID: Rnn2QiFjQdibD9SxqdxFmg== X-CSE-MsgGUID: USCioq/kST2fWBvRHD3vLA== X-IronPort-AV: E=McAfee;i="6800,10657,11583"; a="66378810" X-IronPort-AV: E=Sophos;i="6.19,231,1754982000"; d="scan'208";a="66378810" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by orvoesa107.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Oct 2025 09:25:58 -0700 X-CSE-ConnectionGUID: 4oqxeFpYQJaQbWtbCxrgeA== X-CSE-MsgGUID: J/iikkarTcGc2GuVi06PPw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,231,1754982000"; d="scan'208";a="205919283" Received: from ldmartin-desk2.corp.intel.com (HELO [10.125.111.202]) ([10.125.111.202]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Oct 2025 09:25:56 -0700 Message-ID: <89146527-3f41-4f1e-8511-0d06e169c09e@intel.com> Date: Wed, 15 Oct 2025 09:25:55 -0700 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot ci] Re: Fix stale IOTLB entries for kernel address space To: syzbot ci , akpm@linux-foundation.org, apopple@nvidia.com, baolu.lu@linux.intel.com, bp@alien8.de, dave.hansen@linux.intel.com, david@redhat.com, iommu@lists.linux.dev, jannh@google.com, jean-philippe@linaro.org, jgg@nvidia.com, joro@8bytes.org, kevin.tian@intel.com, liam.howlett@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, luto@kernel.org, mhocko@kernel.org, mingo@redhat.com, peterz@infradead.org, robin.murphy@arm.com, rppt@kernel.org, security@kernel.org, stable@vger.kernel.org, tglx@linutronix.de, urezki@gmail.com, vasant.hegde@amd.com, vbabka@suse.cz, will@kernel.org, willy@infradead.org, x86@kernel.org, yi1.lai@intel.com Cc: syzbot@lists.linux.dev, syzkaller-bugs@googlegroups.com References: <68eeb99e.050a0220.91a22.0220.GAE@google.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Here's the part that confuses me: On 10/14/25 13:59, syzbot ci wrote: > page last free pid 5965 tgid 5964 stack trace: > reset_page_owner include/linux/page_owner.h:25 [inline] > free_pages_prepare mm/page_alloc.c:1394 [inline] > __free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2906 > pmd_free_pte_page+0xa1/0xc0 arch/x86/mm/pgtable.c:783 > vmap_try_huge_pmd mm/vmalloc.c:158 [inline] ... So, vmap_try_huge_pmd() did a pmd_free_pte_page(). Yet, somehow, the PMD stuck around so that it *could* be used after being freed. It _looks_ like pmd_free_pte_page() freed the page, returned 0, and made vmap_try_huge_pmd() return early, skipping the pmd pmd_set_huge(). But I don't know how that could possibly happen.