From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 68D15CAC5B0 for ; Fri, 3 Oct 2025 18:43:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=xHNyfbRZ6FAftCf7527F2xqDMOlX706UesPFKpHNK60=; b=L3e3YCULg5peByxQv2DpzXITY0 NSTh91bR/9P+ON7NS3dN0IIi0LpQtCwtiFTWdEsxalA8FRxrtuPPA9BU2vAe6m770d9WXQiTITzRi amcAUT3y3t5ooBJjBbfW5VYh/mrc8T1rmpHPuvQFW9Ri70ISF9YRxYt1iDXRpLlJn9iKMOHPNW3+Y Oe7Bx1jc4VOCA+reu3pM5gZlN+rDwsJHP5noqiqoTFq+2/xkESarOSJllt/5NgBZ6rRS19lPWzeny 4lxSnHxpDDw6eTOtor7OzdNjRM71pYAraUZera4oQp0MUhINWFvUNij8v+8ZOb9xZIazOcBep/4AT 4tdnMnlw==; 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charset=us-ascii Content-Disposition: inline In-Reply-To: <20251003183917.4209-1-will@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251003_114325_358885_A1E49985 X-CRM114-Status: GOOD ( 11.04 ) 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, Oct 03, 2025 at 07:39:17PM +0100, Will Deacon wrote: > Stable commit 23249dade24e ("KVM: arm64: Fix kernel BUG() due to bad > backport of FPSIMD/SVE/SME fix") fixed a kernel BUG() caused by a bad > backport of upstream commit fbc7e61195e2 ("KVM: arm64: Unconditionally > save+flush host FPSIMD/SVE/SME state") by ensuring that softirqs are > disabled/enabled across the fpsimd register save operation. > > Unfortunately, although this fixes the original issue, it can now lead > to deadlock when re-enabling softirqs causes pending softirqs to be > handled with locks already held: > > | BUG: spinlock recursion on CPU#7, CPU 3/KVM/57616 > | lock: 0xffff3045ef850240, .magic: dead4ead, .owner: CPU 3/KVM/57616, .owner_cpu: 7 > | CPU: 7 PID: 57616 Comm: CPU 3/KVM Tainted: G O 6.1.152 #1 > | Hardware name: SoftIron SoftIron Platform Mainboard/SoftIron Platform Mainboard, BIOS 1.31 May 11 2023 > | Call trace: > | dump_backtrace+0xe4/0x110 > | show_stack+0x20/0x30 > | dump_stack_lvl+0x6c/0x88 > | dump_stack+0x18/0x34 > | spin_dump+0x98/0xac > | do_raw_spin_lock+0x70/0x128 > | _raw_spin_lock+0x18/0x28 > | raw_spin_rq_lock_nested+0x18/0x28 > | update_blocked_averages+0x70/0x550 > | run_rebalance_domains+0x50/0x70 > | handle_softirqs+0x198/0x328 > | __do_softirq+0x1c/0x28 > | ____do_softirq+0x18/0x28 > | call_on_irq_stack+0x30/0x48 > | do_softirq_own_stack+0x24/0x30 > | do_softirq+0x74/0x90 > | __local_bh_enable_ip+0x64/0x80 > | fpsimd_save_and_flush_cpu_state+0x5c/0x68 > | kvm_arch_vcpu_put_fp+0x4c/0x88 > | kvm_arch_vcpu_put+0x28/0x88 > | kvm_sched_out+0x38/0x58 > | __schedule+0x55c/0x6c8 > | schedule+0x60/0xa8 > > Take a tiny step towards the upstream fix in 9b19700e623f ("arm64: > fpsimd: Drop unneeded 'busy' flag") by additionally disabling hardirqs > while saving the fpsimd registers. > > Cc: Ard Biesheuvel > Cc: Lee Jones > Cc: Sasha Levin > Cc: Greg Kroah-Hartman ' here ^^^ and so you didn't end up on CC for this one. Will