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 4AD621EB195; Mon, 6 Oct 2025 10:00:04 +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=1759744809; cv=none; b=HunZ2AAFwvamaM4LdEZ8KOsLZWXefQutF6HuISon5BDKKvl3qFhAcqV+eZ31YNHNsR0xgdhFM1nJxFPtJZxkRovtuJu5puUu+dTgdXsfM4lA6LR/Lf2zALHE4FSHkRpm1O7bgHqMtQVGbgJkwJkA1ywG9lyNp6pyMDUhomQ0ed8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759744809; c=relaxed/simple; bh=HmCN+7Mqf/MRdFKZQf5GfilkUM5v3O6PnYlANxH+lYk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YgUkIOVLTq5FZWWt26PHYRAvlFco8b5GIA/eNoPv6jXB7Jd3ilw7biSG8YN5uDiawl1GNyiXTKN6bK6RNptgkRDRSH/LLt7a86L8ZxsXOMhRm7G168oiDnQtbo2OJxYMWQH9h9A+IH3wQ/nApZaOsgxUVx8OCvkalBBKyhUo0sc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=GcK951BV; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="GcK951BV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 399D7C4CEF7; Mon, 6 Oct 2025 10:00:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1759744804; bh=HmCN+7Mqf/MRdFKZQf5GfilkUM5v3O6PnYlANxH+lYk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GcK951BVY6eNOsq8UkKBT79D/4LwVGMYN73Kh7H+2tp0kYNTImy/2HGvuo7iNrBNW CcLxxOFnGZzkJ/VJxgc1j3YyHhYSNA8MW12qHBkRD73/FXSBMaDudUAlAseSbVChCc /uXyC9ofKpzwzwAScFaRTD7qXRah83XPIq5TREdE= Date: Mon, 6 Oct 2025 12:00:02 +0200 From: Greg KH To: Will Deacon Cc: stable@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, Ard Biesheuvel , Lee Jones , Sasha Levin , Kenneth Van Alstyne Subject: Re: [STABLE 5.15.y] [PATCH] KVM: arm64: Fix softirq masking in FPSIMD register saving sequence Message-ID: <2025100641-guileless-retainer-c885@gregkh> References: <20251003183917.4209-1-will@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Oct 03, 2025 at 07:43:19PM +0100, Will Deacon wrote: > 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 > Sorry, Greg, I lost a stray '>' here ^^^ and so you didn't end up on CC > for this one. No worries, I see the stuff going to stable@vger.kernel.org as well :) Now all queued up, thanks for these. greg k-h