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 52615CCA471 for ; Fri, 3 Oct 2025 18:40:35 +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:Content-Transfer-Encoding: MIME-Version:Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-Type: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Owner; bh=NfsEZ8B1aMDxLol27Z2fvgh5llxLpGCuODjRV+PoYDU=; b=zQOllImLAQ9ohK6+G1wScJbLT8 qlI2LfuvDc/TChiAEiyN9wTS5QRhb0XMRWq3PlLJhGsETenShPzuHmjQUYQac/IJ1MVhxIYv/2J9t 2TUiJy1gIx0As3bB5SfqM66pBqHkCPtvPPMMemZSMsEVs+FCat8M5gBtthgYfe5NL4w/Q5hgxDYt+ pPhgVWy9UTSHnOnr/QrMACFVOBoGEx/uz18WDlTAPkRBfn6gl1YE1tkCqNf/e5ZiF54tQsrPb+yVI U6z+Mc7Ca+EobHA6C9zfFwSGarl4r+heEI4dj1Qi++WlwFZUpuOtkgNorlnYVg/sbt3jqPIBna3tE GcZBqHDg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1v4khi-0000000CwKs-0gLQ; Fri, 03 Oct 2025 18:40:30 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1v4khh-0000000CwKh-1nvo for linux-arm-kernel@lists.infradead.org; Fri, 03 Oct 2025 18:40:29 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 8BE5460215; Fri, 3 Oct 2025 18:40:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 59EF3C4CEF5; Fri, 3 Oct 2025 18:40:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1759516828; bh=jmWoLxGdvgZIEzoFN4sKOqTG7UUYTTku1IhoUrAB+lg=; h=From:To:Cc:Subject:Date:From; b=FaCmS1ullccxRzbFtKoPIFjlfDaHjSHaWcsDrvBfAuJErEzu6hRAwvzA9hgAkQMBf FhhOy+2PXdyWBhnwSJJfQx+Tq5mKhpOxLykVm5ekERcwEqWLlWRWXJNbFja4Tsf6j/ L2IgX4e0OJgXlOwJ5S90Up/K03IcyQEqe1KJoWsVIQv5t/6KiWdWUesXC3kre/1xas OkfZ1AiKVVN6BMIWLI5RG1qYqzYbPPhG60RtYVRNz+jyV5yOU/U02+tH0rDKX6o9WM xgvgT94QMXl/GvDzT7xLPPVTfLvaBFUStgFhmLd7cngsGrtjpeXriJ3/YkbfJouioa HH7ezdX9gMT7Q== From: Will Deacon To: stable@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, Will Deacon , Ard Biesheuvel , Lee Jones , Sasha Levin , Greg Kroah-Hartman , Kenneth Van Alstyne Subject: [STABLE 6.1.y] [PATCH] KVM: arm64: Fix softirq masking in FPSIMD register saving sequence Date: Fri, 3 Oct 2025 19:40:18 +0100 Message-Id: <20251003184018.4264-1-will@kernel.org> X-Mailer: git-send-email 2.39.5 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 Stable commit 8f4dc4e54eed ("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 Cc: # 6.1.y Fixes: 8f4dc4e54eed ("KVM: arm64: Fix kernel BUG() due to bad backport of FPSIMD/SVE/SME fix") Reported-by: Kenneth Van Alstyne Link: https://lore.kernel.org/r/010001999bae0958-4d80d25d-8dda-4006-a6b9-798f3e774f6c-000000@email.amazonses.com Signed-off-by: Will Deacon --- arch/arm64/kernel/fpsimd.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index bc42163a7fd1..62780cf901dc 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -1848,13 +1848,17 @@ static void fpsimd_flush_cpu_state(void) */ void fpsimd_save_and_flush_cpu_state(void) { + unsigned long flags; + if (!system_supports_fpsimd()) return; WARN_ON(preemptible()); - get_cpu_fpsimd_context(); + local_irq_save(flags); + __get_cpu_fpsimd_context(); fpsimd_save(); fpsimd_flush_cpu_state(); - put_cpu_fpsimd_context(); + __put_cpu_fpsimd_context(); + local_irq_restore(flags); } #ifdef CONFIG_KERNEL_MODE_NEON -- 2.51.0.618.g983fd99d29-goog