From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: nVMX: Shadowing of CPU_BASED_VM_EXEC_CONTROL broken Date: Wed, 08 Oct 2014 18:07:39 +0200 Message-ID: <5435614B.3020305@siemens.com> References: <5434F5F9.3030803@siemens.com> <20141008092539.GA16561@kernel> <5435092A.3090704@siemens.com> <54350FD4.10403@redhat.com> <543511FE.3060108@siemens.com> <54351336.4030005@redhat.com> <54355344.5050301@siemens.com> <54355BD9.3010201@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: kvm , Bandan Das To: Paolo Bonzini , Wanpeng Li Return-path: Received: from thoth.sbs.de ([192.35.17.2]:41157 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752503AbaJHQII (ORCPT ); Wed, 8 Oct 2014 12:08:08 -0400 In-Reply-To: <54355BD9.3010201@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2014-10-08 17:44, Paolo Bonzini wrote: > Il 08/10/2014 17:07, Jan Kiszka ha scritto: >> As usual, this was a nasty race that involved some concurrent VCPUs and >> proper host load, so hard to write unit tests... >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index 04fa1b8..d6bcaca 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -6417,6 +6417,8 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx) >> const unsigned long *fields = shadow_read_write_fields; >> const int num_fields = max_shadow_read_write_fields; >> >> + preempt_disable(); >> + >> vmcs_load(shadow_vmcs); >> >> for (i = 0; i < num_fields; i++) { >> @@ -6440,6 +6442,8 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx) >> >> vmcs_clear(shadow_vmcs); >> vmcs_load(vmx->loaded_vmcs->vmcs); >> + >> + preempt_enable(); >> } >> >> static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) >> @@ -6457,6 +6461,8 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) >> u64 field_value = 0; >> struct vmcs *shadow_vmcs = vmx->nested.current_shadow_vmcs; >> >> + preempt_disable(); >> + >> vmcs_load(shadow_vmcs); >> >> for (q = 0; q < ARRAY_SIZE(fields); q++) { >> @@ -6483,6 +6489,8 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) >> >> vmcs_clear(shadow_vmcs); >> vmcs_load(vmx->loaded_vmcs->vmcs); >> + >> + preempt_enable(); >> } >> >> No proper patch yet because there might be a smarter approach without >> using the preempt_disable() hammer. > > copy_vmcs12_to_shadow already runs with preemption disabled; for stable@ > it's not that bad to do the same in copy_shadow_to_vmcs12. > > For 3.18 it could be nice of course to use loaded_vmcs properly, but it > would also incur some overhead. If the other direction is already under preempt_disable, I'm not sure if there is much to gain for this direction. Anyway, fix sent. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux