From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH v7 01/15] nEPT: Support LOAD_IA32_EFER entry/exit controls for L1 Date: Tue, 6 Aug 2013 11:00:51 +0300 Message-ID: <20130806080051.GB8218@redhat.com> References: <1375690040-5764-1-git-send-email-gleb@redhat.com> <1375690040-5764-2-git-send-email-gleb@redhat.com> <20130805114032.GE10891@redhat.com> <5200AA0B.5080409@web.de> <20130806075109.GA8218@redhat.com> <5200ABDD.5050307@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Arthur Chunqi Li , kvm , Xiao Guangrong , Jun Nakajima , Yang Zhang , Paolo Bonzini To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:3341 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751608Ab3HFIA4 (ORCPT ); Tue, 6 Aug 2013 04:00:56 -0400 Content-Disposition: inline In-Reply-To: <5200ABDD.5050307@web.de> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Aug 06, 2013 at 09:55:09AM +0200, Jan Kiszka wrote: > On 2013-08-06 09:51, Gleb Natapov wrote: > > On Tue, Aug 06, 2013 at 09:47:23AM +0200, Jan Kiszka wrote: > >> On 2013-08-05 13:40, Gleb Natapov wrote: > >>> On Mon, Aug 05, 2013 at 07:27:33PM +0800, Arthur Chunqi Li wrote: > >>>> On Mon, Aug 5, 2013 at 4:07 PM, Gleb Natapov wrote: > >>>>> From: Nadav Har'El > >>>>> > >>>>> Recent KVM, since http://kerneltrap.org/mailarchive/linux-kvm/2010/5/2/6261577 > >>>>> switch the EFER MSR when EPT is used and the host and guest have different > >>>>> NX bits. So if we add support for nested EPT (L1 guest using EPT to run L2) > >>>>> and want to be able to run recent KVM as L1, we need to allow L1 to use this > >>>>> EFER switching feature. > >>>>> > >>>>> To do this EFER switching, KVM uses VM_ENTRY/EXIT_LOAD_IA32_EFER if available, > >>>>> and if it isn't, it uses the generic VM_ENTRY/EXIT_MSR_LOAD. This patch adds > >>>>> support for the former (the latter is still unsupported). > >>>>> > >>>>> Nested entry and exit emulation (prepare_vmcs_02 and load_vmcs12_host_state, > >>>>> respectively) already handled VM_ENTRY/EXIT_LOAD_IA32_EFER correctly. So all > >>>>> that's left to do in this patch is to properly advertise this feature to L1. > >>>>> > >>>>> Note that vmcs12's VM_ENTRY/EXIT_LOAD_IA32_EFER are emulated by L0, by using > >>>>> vmx_set_efer (which itself sets one of several vmcs02 fields), so we always > >>>>> support this feature, regardless of whether the host supports it. > >>>>> > >>>>> Reviewed-by: Orit Wasserman > >>>>> Signed-off-by: Nadav Har'El > >>>>> Signed-off-by: Jun Nakajima > >>>>> Signed-off-by: Xinhao Xu > >>>>> Signed-off-by: Yang Zhang > >>>>> Signed-off-by: Gleb Natapov > >>>>> --- > >>>>> arch/x86/kvm/vmx.c | 23 ++++++++++++++++------- > >>>>> 1 file changed, 16 insertions(+), 7 deletions(-) > >>>>> > >>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > >>>>> index e999dc7..27efa6a 100644 > >>>>> --- a/arch/x86/kvm/vmx.c > >>>>> +++ b/arch/x86/kvm/vmx.c > >>>>> @@ -2198,7 +2198,8 @@ static __init void nested_vmx_setup_ctls_msrs(void) > >>>>> #else > >>>>> nested_vmx_exit_ctls_high = 0; > >>>>> #endif > >>>>> - nested_vmx_exit_ctls_high |= VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR; > >>>>> + nested_vmx_exit_ctls_high |= (VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR | > >>>>> + VM_EXIT_LOAD_IA32_EFER); > >>>> Gleb, why we don't need to check whether host supports > >>>> VM_EXIT_LOAD_IA32_EFER here, as what you noted in my > >>>> VM_EXIT_LOAD_IA32_PAT patch? > >>> Nested VMX completely emulates the capability. > >> > >> No, it doesn't. The values for host/guest are handled over via the > >> corresponding VMCS fields, physically, even though the actual loading is > >> emulated then. So we must not expose this feature unconditionally. > > Can you show me the code where it happens? > > When the guest writes to HOST/GUEST_IA32_EFER, we will store this in the > vmcs that will then become the active one on next L1/L2 entry, no? > Guest writes are stored in vmcs12 which is not HW vmcs, just a format kvm uses internally (see vmcs12_write_any). During guest entry vmcs02 is constructed from vmcs12 (see prepare_vmcs02) and this function does not access HOST/GUEST_IA32_EFER directly, it uses vmx_set_efer instead which takes care of things. Same function access GUEST_IA32_PAT directly though. -- Gleb.