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Fri, 19 Sep 2025 14:26:58 +0000 Date: Fri, 19 Sep 2025 15:26:58 +0100 Message-ID: <871po2zff1.wl-maz@kernel.org> From: Marc Zyngier To: syzbot Cc: catalin.marinas@arm.com, joey.gouly@arm.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, oliver.upton@linux.dev, suzuki.poulose@arm.com, syzkaller-bugs@googlegroups.com, will@kernel.org, yuzenghui@huawei.com Subject: Re: [syzbot] [kvmarm?] kernel BUG in kvm_s2_put_page In-Reply-To: <68cd66b0.050a0220.139b6.000f.GAE@google.com> References: <68cd66b0.050a0220.139b6.000f.GAE@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: syzbot+c41f3ddb8299a30a98b5@syzkaller.appspotmail.com, catalin.marinas@arm.com, joey.gouly@arm.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, oliver.upton@linux.dev, suzuki.poulose@arm.com, syzkaller-bugs@googlegroups.com, will@kernel.org, yuzenghui@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250919_072701_486836_6AAD88C9 X-CRM114-Status: GOOD ( 16.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 19 Sep 2025 15:20:32 +0100, syzbot wrote: > > Hello, > > syzbot found the following issue on: > > HEAD commit: 62e68218ab58 Merge branch kvm-arm64/nv-debug into kvmarm-m.. > git tree: git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm.git next > console output: https://syzkaller.appspot.com/x/log.txt?x=1551cf62580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=1b1bafe30fc85201 > dashboard link: https://syzkaller.appspot.com/bug?extid=c41f3ddb8299a30a98b5 > compiler: Debian clang version 20.1.8 (++20250708123704+0de59a293f7a-1~exp1~20250708003721.134), Debian LLD 20.1.8 > userspace arch: arm64 > > Unfortunately, I don't have any reproducer for this issue yet. > > Downloadable assets: > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/fa3fbcfdac58/non_bootable_disk-62e68218.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/99c4e665c20d/vmlinux-62e68218.xz > kernel image: https://storage.googleapis.com/syzbot-assets/4204d63db4b5/Image-62e68218.gz.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+c41f3ddb8299a30a98b5@syzkaller.appspotmail.com > > raw: 01ffea8000000000 ffffc1ffc0807c48 ffffc1ffc080a888 0000000000000000 > raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 > page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) > ------------[ cut here ]------------ > kernel BUG at ./include/linux/mm.h:1036! > Internal error: Oops - BUG: 00000000f2000800 [#1] SMP > Modules linked in: > CPU: 0 UID: 0 PID: 4079 Comm: syz.1.200 Not tainted syzkaller #0 PREEMPT > Hardware name: linux,dummy-virt (DT) > pstate: 60402009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > pc : put_page_testzero include/linux/mm.h:1036 [inline] > pc : folio_put_testzero include/linux/mm.h:1042 [inline] > pc : folio_put include/linux/mm.h:1359 [inline] > pc : put_page include/linux/mm.h:1429 [inline] > pc : kvm_s2_put_page+0x374/0x3a0 arch/arm64/kvm/mmu.c:264 > lr : put_page_testzero include/linux/mm.h:1036 [inline] > lr : folio_put_testzero include/linux/mm.h:1042 [inline] > lr : folio_put include/linux/mm.h:1359 [inline] > lr : put_page include/linux/mm.h:1429 [inline] > lr : kvm_s2_put_page+0x374/0x3a0 arch/arm64/kvm/mmu.c:264 This is likely caused by the S2 refcounting issue that has just been reverted in Linus' tree, and that is not in the kvmarm/next branch. M. -- Jazz isn't dead. It just smells funny.