From patchwork Fri Jan 25 15:40:51 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 10781559 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id C8CB1139A for ; Fri, 25 Jan 2019 15:41:50 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B88BA2F750 for ; Fri, 25 Jan 2019 15:41:50 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id AD1FB2FA05; Fri, 25 Jan 2019 15:41:50 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 429262F750 for ; Fri, 25 Jan 2019 15:41:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728736AbfAYPlt (ORCPT ); Fri, 25 Jan 2019 10:41:49 -0500 Received: from mga09.intel.com ([134.134.136.24]:54654 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727826AbfAYPls (ORCPT ); Fri, 25 Jan 2019 10:41:48 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 25 Jan 2019 07:41:46 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,521,1539673200"; d="scan'208";a="128877871" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.14]) by orsmga002.jf.intel.com with ESMTP; 25 Jan 2019 07:41:46 -0800 From: Sean Christopherson To: Paolo Bonzini , =?utf-8?b?UmFkaW0gS3LEjW3DocWZ?= Cc: kvm@vger.kernel.org, Jim Mattson , Konrad Rzeszutek Wilk Subject: [PATCH v3 04/33] KVM: VMX: Modify only RSP when creating a placeholder for guest's RCX Date: Fri, 25 Jan 2019 07:40:51 -0800 Message-Id: <20190125154120.19385-5-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190125154120.19385-1-sean.j.christopherson@intel.com> References: <20190125154120.19385-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP In the vCPU-run asm blob, the guest's RCX is temporarily saved onto the stack after VM-Exit as the exit flow must first load a register with a pointer to the vCPU's save area in order to save the guest's registers. RCX is arbitrarily designated as the scratch register. Since the stack usage is to (1)save host, (2)save guest, (3)load host and (4)load guest, the code can't conform to the stack's natural FIFO semantics, i.e. it can't simply do PUSH/POP. Regardless of whether it is done for the host's value or guest's value, at some point the code needs to access the stack using a non-traditional method, e.g. MOV instead of POP. vCPU-run opts to create a placeholder on the stack for guest's RCX (by adjusting RSP) and saves RCX to its place immediately after VM-Exit (via MOV). In other words, the purpose of the first 'PUSH RCX' at the start of the vCPU-run asm blob is to adjust RSP down, i.e. there's no need to actually access memory. Use 'SUB $wordsize, RSP' instead of 'PUSH RCX' to make it more obvious that the intent is simply to create a gap on the stack for the guest's RCX. Reviewed-by: Jim Mattson Reviewed-by: Konrad Rzeszutek Wilk Signed-off-by: Sean Christopherson --- arch/x86/kvm/vmx/vmx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index a8de1d7f06e1..45a7cda813c8 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6377,7 +6377,7 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx) asm( /* Store host registers */ "push %%" _ASM_DX "; push %%" _ASM_BP ";" - "push %%" _ASM_CX " \n\t" /* placeholder for guest rcx */ + "sub $%c[wordsize], %%" _ASM_SP "\n\t" /* placeholder for guest RCX */ "push %%" _ASM_CX " \n\t" "sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */ "cmp %%" _ASM_SP ", %c[host_rsp](%%" _ASM_CX ") \n\t"