From mboxrd@z Thu Jan 1 00:00:00 1970 From: Liran Alon Subject: Re: [PATCH v2] KVM: nVMX/nSVM: Don't intercept #UD when running L2 Date: Sat, 02 Dec 2017 02:27:03 +0200 Message-ID: <5A21F357.4080108@ORACLE.COM> References: <1509977710-29704-1-git-send-email-liran.alon@oracle.com> <20171110213740.GD2189@flask> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Cc: Paolo Bonzini , kvm list , Idan Brown , Konrad Rzeszutek Wilk To: Jim Mattson , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:37876 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751596AbdLBA1M (ORCPT ); Fri, 1 Dec 2017 19:27:12 -0500 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 02/12/17 01:00, Jim Mattson wrote: > How does this change interact with commit 84cffe499b94 ("kvm: Emulate MOVBE")? > > If the hardware doesn't support MOVBE, but L0 sets CPUID.01H:ECX.MOVBE > in L1's emulated CPUID information, then L1 is likely to pass that > CPUID bit through to L2. L2 will expect MOVBE to work, but if L1 > doesn't intercept #UD, then any MOVBE instruction executed in L2 will > raise #UD, and the exception will be delivered in L2. > Nice catch. When I considered the functionality of the original commit which I attempted to fix (commit ae1f57670703 ("KVM: nVMX: Do not emulate #UD while in guest mode")), my patch made sense as a more complete and better fix. However, both my patch and the original patch don't seem to consider the issue you present here. I completely agree. Maybe it was better just reverting my patch and commit ae1f57670703. I think the attempt of that patch was to make L0 not simulate behaviour it simulates for L1 in L2 as-well. but after reading your reply, I think that it is a desired behaviour... -Liran > > On Fri, Nov 10, 2017 at 1:37 PM, Radim Krčmář wrote: >> 2017-11-06 16:15+0200, Liran Alon: >>> When running L2, #UD should be intercepted by L1 or just forwarded >>> directly to L2. It should not reach L0 x86 emulator. >>> Therefore, set intercept for #UD only based on L1 exception-bitmap. >>> >>> Also add WARN_ON_ONCE() on L0 #UD intercept handlers to make sure >>> it is never reached while running L2. >>> >>> This improves commit ae1f57670703 ("KVM: nVMX: Do not emulate #UD while >>> in guest mode") by removing an unnecessary exit from L2 to L0 on #UD >>> when L1 doesn't intercept it. >>> >>> In addition, SVM L0 #UD intercept handler doesn't handle correctly the >>> case it is raised from L2. In this case, it should forward the #UD to >>> guest instead of x86 emulator. As done in VMX #UD intercept handler. >>> This commit fixes this issue as-well. >>> >>> Signed-off-by: Liran Alon >>> Reviewed-by: Nikita Leshenko >>> Reviewed-by: Konrad Rzeszutek Wilk >>> Signed-off-by: Konrad Rzeszutek Wilk >>> --- >> >> Applied, thanks.