From patchwork Mon Dec 9 20:05:17 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 11280363 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 52DF1138D for ; Mon, 9 Dec 2019 20:13:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3BC1D222C4 for ; Mon, 9 Dec 2019 20:13:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726911AbfLIUNP (ORCPT ); Mon, 9 Dec 2019 15:13:15 -0500 Received: from mga12.intel.com ([192.55.52.136]:20612 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726230AbfLIUNP (ORCPT ); Mon, 9 Dec 2019 15:13:15 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 09 Dec 2019 12:05:18 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,296,1571727600"; d="scan'208";a="387357088" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.202]) by orsmga005.jf.intel.com with ESMTP; 09 Dec 2019 12:05:18 -0800 From: Sean Christopherson To: Paolo Bonzini , =?utf-8?b?UmFkaW0gS3LEjW3DocWZ?= Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] KVM: x86: Add a WARN on TIF_NEED_FPU_LOAD in kvm_load_guest_fpu() Date: Mon, 9 Dec 2019 12:05:17 -0800 Message-Id: <20191209200517.13382-1-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.24.0 MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org WARN once in kvm_load_guest_fpu() if TIF_NEED_FPU_LOAD is observed, as that would mean that KVM is corrupting userspace's FPU by saving unknown register state into arch.user_fpu. Add a comment to explain why KVM WARNs on TIF_NEED_FPU_LOAD instead of implementing logic similar to fpu__copy(). Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3ed167e039e5..f2c8a053b017 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8474,6 +8474,13 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu) { fpregs_lock(); + /* + * Reloading userspace's FPU is handled by kvm_arch_vcpu_load(), both + * for direct calls from userspace (via vcpu_load()) and if this task + * is preempted (via kvm_arch_sched_in()) between vcpu_load() and now. + */ + WARN_ON_ONCE(test_thread_flag(TIF_NEED_FPU_LOAD)); + copy_fpregs_to_fpstate(vcpu->arch.user_fpu); /* PKRU is separately restored in kvm_x86_ops->run. */ __copy_kernel_to_fpregs(&vcpu->arch.guest_fpu->state,