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 3D41C352091; Tue, 26 Aug 2025 14:00:45 +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=1756216845; cv=none; b=VC9KgggfheU7NAWQWpi8NZBvF+g4zb00fllS5p6AOPi06VolIuLs4v9H77dUOYOfhM8nuXkE5P/ytmiUDKXLgbJsRrWXjUHWTkdbdNRKXsVuo/v1Sr4TkmOvvOQU/MKduQO9ydw2AyfSY/0aDna5FfpQdBN0mut4n3ZR6fQqNAs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756216845; c=relaxed/simple; bh=V/hPTiwurgozOMoxEqB/PmOEKYCTPVAeJw89J5JXCEE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YnSpKy4YV9eZrh38IN7Dr7zMndR6xHv3tZ6Q26XCiFCiRMII83piq4zqhQ6XrhnVsfQfOctzN0CbF/onoODeN4mnj5Td3/aSwx/35GdSy1m4phLzLbDKx7B3w2xFSFXyFU3Jbp+wnaXz7/5xurund6BGL3+nme+AhGPX5MD+OUU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=0MP7ppqC; 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="0MP7ppqC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C3338C4CEF1; Tue, 26 Aug 2025 14:00:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1756216845; bh=V/hPTiwurgozOMoxEqB/PmOEKYCTPVAeJw89J5JXCEE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=0MP7ppqCT/VI/ZMExYVJo7mEb2YpD8xA8ZLPj5/xz1D87FzNCdHYYbWtvHExJvPVH 11gLcjK9VecmO6sAU5QbAxv6/XMkOOo1D0yZsiiODHeCiy/gGhlq2c0pp0K4olrrCm zaviDDbPwYfHojnaVfhO0mHC+NDicvRr/akBjcWk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ard Biesheuvel , Lee Jones , Sasha Levin , Mark Rutland , Fuad Tabba , Marc Zyngier , Will Deacon Subject: [PATCH 5.15 563/644] KVM: arm64: Fix kernel BUG() due to bad backport of FPSIMD/SVE/SME fix Date: Tue, 26 Aug 2025 13:10:54 +0200 Message-ID: <20250826111000.481457567@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250826110946.507083938@linuxfoundation.org> References: <20250826110946.507083938@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Will Deacon Upstream commit fbc7e61195e2 ("KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state") relies on interrupts being disabled during fpsimd_save_and_flush_cpu_state() so that a softirq cannot be taken while the host floating point context is being saved and potentially try to use kernel-mode NEON. Unfortunately, stable kernels without 9b19700e623f ("arm64: fpsimd: Drop unneeded 'busy' flag") leave interrupts enabled in fpsimd_save_and_flush_cpu_state() and so the BUG_ON(!may_use_simd()) in kernel_neon_begin() has been observed to trigger in real-world usage: | kernel BUG at arch/arm64/kernel/fpsimd.c:1904! | Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP | | Call trace: | kernel_neon_begin+0xdc/0x12c | ... | crypto_aead_decrypt+0x5c/0x6c | seqiv_aead_decrypt+0x88/0x9c | crypto_aead_decrypt+0x5c/0x6c | esp_input+0x280/0x364 | xfrm_input+0x6ac/0x16f8 | ... | net_rx_action+0x13c/0x31c | handle_softirqs+0x124/0x3d0 | __do_softirq+0x14/0x20 | ____do_softirq+0x10/0x20 | call_on_irq_stack+0x3c/0x74 | do_softirq_own_stack+0x1c/0x2c | __irq_exit_rcu+0x54/0xb4 | irq_exit_rcu+0x10/0x1c | el1_interrupt+0x38/0x58 | el1h_64_irq_handler+0x18/0x24 | el1h_64_irq+0x68/0x6c | fpsimd_save+0xe4/0x130 | kvm_arch_vcpu_load_fp+0x2c/0x58 | kvm_arch_vcpu_load+0x88/0x26c | kvm_sched_in+0x2c/0x3c Given that 9b19700e623f ("arm64: fpsimd: Drop unneeded 'busy' flag") is not a fix in its own right, has non-trivial dependencies and is a reasonably invasive change to the in-kernel use of fpsimd, opt instead for a simple fix to use the softirq-safe {get,put}_cpu_fpsimd_context() helpers in fpsimd_save_and_flush_cpu_state(). Cc: Ard Biesheuvel Cc: Lee Jones Cc: Sasha Levin Cc: Mark Rutland Cc: Fuad Tabba Cc: Marc Zyngier Cc: # 5.15.y, 6.1.y and 6.6.y Fixes: 806d5c1e1d2e ("KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state") # 6.6.y Fixes: 04c50cc23a49 ("KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state") # 6.1.y Fixes: 5289ac43b69c ("KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state") # 5.15.y Signed-off-by: Will Deacon Signed-off-by: Greg Kroah-Hartman --- arch/arm64/kernel/fpsimd.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -1303,10 +1303,10 @@ void fpsimd_save_and_flush_cpu_state(voi if (!system_supports_fpsimd()) return; WARN_ON(preemptible()); - __get_cpu_fpsimd_context(); + get_cpu_fpsimd_context(); fpsimd_save(); fpsimd_flush_cpu_state(); - __put_cpu_fpsimd_context(); + put_cpu_fpsimd_context(); } #ifdef CONFIG_KERNEL_MODE_NEON