From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 63CBF1F0991; Fri, 3 Oct 2025 18:40:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759516828; cv=none; b=TJYaeAsI+C/i+AoM6Wx75Uuh+lrkmUGTuUvm/+tzKzkfjz3kwO1A6+4uiNl+3+mbRLb9Fn5jdrAoibtgxjSddgPEqkgo/eiWXyd9hu5DZ0WnJX0ctbOSlXTzu1+lNUPizHQjVZM4hF03Y904UKSPKNYxPdxwpwV6SJXXvQT+rYo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759516828; c=relaxed/simple; bh=jmWoLxGdvgZIEzoFN4sKOqTG7UUYTTku1IhoUrAB+lg=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=jZnZMDTln6PXfkXHasJ0ei3etkXlOk8Dtbkx3wgb0GqbOL4zIlIwgmQM0cq8nze7+8Guq+7eng5NOLBLLZoN2dkq8Z6J9cxPzH54vlDPlamuY5r/pA4UJc5nl48CWndtomI9UA2CQdYiIylhlUunYwtr2410sHjagj9dX9bNk/M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FaCmS1ul; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="FaCmS1ul" 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 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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