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 <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? > > 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. -- 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
