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 25884227EA8; Tue, 26 Aug 2025 13:31:55 +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=1756215115; cv=none; b=ea2YH6mwnuQhnIE8YS5CM0OHlI+uIH7PhAp1zHic3kiKukwP8TdnnmWoqEDPnwsqLt3zjGVzg/6INylZ08sb1+9AOhit84eyZ54LnjEqKCjWs9jeGXmZBJA19YdCOkm3yYMfjTDijUGOa9Bhhq+5T8m5chxdSZHcHy3FA8JgtXs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756215115; c=relaxed/simple; bh=BNnK53uPRK+y6Ogr0SsL6W3MPNd+3DzY3I0kY5gQt/o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=reLD/aOndWQt61bLR8S2r3WC3F6Kxa5/mcQ6O+ix4UvfH3xiSJLQ471zfp4dMd5ibRwPX4TeHCZpLVwutp1buqCSD4k5zIWRNaoXaHzlQoC9/y+LhL7WUJ/ATOSk0IYU7F8w/+Vg2oB4H1B5cnr6wP3JQSv9mztoNcH18NOrWOs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=xlqjffOD; 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="xlqjffOD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 85D56C4CEF1; Tue, 26 Aug 2025 13:31:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1756215115; bh=BNnK53uPRK+y6Ogr0SsL6W3MPNd+3DzY3I0kY5gQt/o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xlqjffODvAoNlO5vCBMv9Z03j+UIxoOhLsZyXmVOTUsj3nbyOXvN3nx5u49aeMzcV trkA7Y9PbTxSuh80F+vwAIBvqwG75rEjfU/uEGV0iHuMuUPzM7+QrJxKDC+fOWWiOE Ez6pqizIuB9w7xwdB2ZydbLSRagFH4cCI/0Z5WIs= 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 6.1 393/482] KVM: arm64: Fix kernel BUG() due to bad backport of FPSIMD/SVE/SME fix Date: Tue, 26 Aug 2025 13:10:46 +0200 Message-ID: <20250826110940.538650326@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250826110930.769259449@linuxfoundation.org> References: <20250826110930.769259449@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 6.1-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 @@ -1851,10 +1851,10 @@ 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