From patchwork Mon Mar 14 11:34:40 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 551387 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 13686C433EF for ; Mon, 14 Mar 2022 11:43:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239478AbiCNLo7 (ORCPT ); Mon, 14 Mar 2022 07:44:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41564 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239527AbiCNLmr (ORCPT ); Mon, 14 Mar 2022 07:42:47 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 624E23BA4E; Mon, 14 Mar 2022 04:40:11 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 0942CB80DC4; Mon, 14 Mar 2022 11:40:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 667D9C340EC; Mon, 14 Mar 2022 11:40:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1647258009; bh=cLHQDXAZOpyLaLgN179kv4tfiwa3d6XUTCrpezCTBoQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=U1fHlND19THm0CdVVZsYheUk+NgsQYyDqmqj57KEVtPkOiHw6XjSMyGVc0RpdSdCy FfU+EPgBTHqdtnJCZUb6lirnvfQQRG00WOKQDzvzBf2JTXn0pbuMNg4nUc6n8F5ABb 7C3HHVnBlK4hTds/oGlnGgOkL7FHCcnkdNMNkjS8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, James Morse Subject: [PATCH 4.19 22/30] KVM: arm64: Reset PMC_EL0 to avoid a panic() on systems with no PMU Date: Mon, 14 Mar 2022 12:34:40 +0100 Message-Id: <20220314112732.412975093@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220314112731.785042288@linuxfoundation.org> References: <20220314112731.785042288@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: James Morse The logic in commit 2a5f1b67ec57 "KVM: arm64: Don't access PMCR_EL0 when no PMU is available" relies on an empty reset handler being benign. This was not the case in earlier kernel versions, so the stable backport of this patch is causing problems. KVMs behaviour in this area changed over time. In particular, prior to commit 03fdfb269009 ("KVM: arm64: Don't write junk to sysregs on reset"), an empty reset handler will trigger a warning, as the guest registers have been poisoned. Prior to commit 20589c8cc47d ("arm/arm64: KVM: Don't panic on failure to properly reset system registers"), this warning was a panic(). Instead of reverting the backport, make it write 0 to the sys_reg[] array. This keeps the reset logic happy, and the dodgy value can't be seen by the guest as it can't request the emulation. The original bug was accessing the PMCR_EL0 register on CPUs that don't implement that feature. There is no known silicon that does this, but v4.9's ACPI support is unable to find the PMU, so triggers this code: | Kernel panic - not syncing: Didn't reset vcpu_sys_reg(24) | CPU: 1 PID: 3055 Comm: lkvm Not tainted 4.9.302-00032-g64e078a56789 #13476 | Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Jul 30 2018 | Call trace: | [] dump_backtrace+0x0/0x1a0 | [] show_stack+0x14/0x20 | [] dump_stack+0x98/0xb8 | [] panic+0x118/0x274 | [] access_actlr+0x0/0x20 | [] kvm_reset_vcpu+0x5c/0xac | [] kvm_arch_vcpu_ioctl+0x3e4/0x490 | [] kvm_vcpu_ioctl+0x5b8/0x720 | [] do_vfs_ioctl+0x2f4/0x884 | [] SyS_ioctl+0x78/0x9c | [] __sys_trace_return+0x0/0x4 Cc: # < v5.3 with 2a5f1b67ec57 backported Signed-off-by: James Morse Signed-off-by: Greg Kroah-Hartman --- arch/arm64/kvm/sys_regs.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -620,8 +620,10 @@ static void reset_pmcr(struct kvm_vcpu * u64 pmcr, val; /* No PMU available, PMCR_EL0 may UNDEF... */ - if (!kvm_arm_support_pmu_v3()) + if (!kvm_arm_support_pmu_v3()) { + vcpu_sys_reg(vcpu, PMCR_EL0) = 0; return; + } pmcr = read_sysreg(pmcr_el0); /*