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 <gleb@xxxxxxxxxx> wrote: > >>> From: Nadav Har'El <nyh@xxxxxxxxxx> > >>> > >>> 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 <owasserm@xxxxxxxxxx> > >>> Signed-off-by: Nadav Har'El <nyh@xxxxxxxxxx> > >>> Signed-off-by: Jun Nakajima <jun.nakajima@xxxxxxxxx> > >>> Signed-off-by: Xinhao Xu <xinhao.xu@xxxxxxxxx> > >>> Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx> > >>> Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx> > >>> --- > >>> 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? > That's the same pattern as with PAT, Arthur is right. > > I've a patch on top of v7 to fix this (and also the incorrect > VM_ENTRY_IA32E_MODE reporting on 32-bit). Will post it soon as part of > an updated version of my unrestricted guest mode series. > > Jan > > -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
