From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: [PATCH 06/13] KVM: VMX: Allow vm86 virtualization of big real mode Date: Tue, 21 Aug 2012 17:07:03 +0300 Message-ID: <1345558030-29370-7-git-send-email-avi@redhat.com> References: <1345558030-29370-1-git-send-email-avi@redhat.com> Cc: kvm@vger.kernel.org To: Marcelo Tosatti Return-path: Received: from mx1.redhat.com ([209.132.183.28]:51456 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754339Ab2HUOHo (ORCPT ); Tue, 21 Aug 2012 10:07:44 -0400 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q7LE7ibS006006 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 21 Aug 2012 10:07:44 -0400 In-Reply-To: <1345558030-29370-1-git-send-email-avi@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Usually, big real mode uses large (4GB) segments. Currently we don't virtualize this; if any segment has a limit other than 0xffff, we emulate. But if we set the vmx-visible limit to 0xffff, we can use vm86 to virtualize real mode; if an access overruns the segment limit, the guest will #GP, which we will trap and forward to the emulator. This results in significantly faster execution, and less risk of hitting an unemulated instruction. If the limit is less than 0xffff, we retain the existing behaviour. Signed-off-by: Avi Kivity --- arch/x86/kvm/vmx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 4f3d6ac..939e4a0 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -3316,7 +3316,7 @@ static bool rmode_segment_valid(struct kvm_vcpu *vcpu, int seg) if (var.base != (var.selector << 4)) return false; - if (var.limit != 0xffff) + if (var.limit < 0xffff) return false; if ((ar | (3 << AR_DPL_SHIFT)) != 0xf3) return false; -- 1.7.11.3