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? Jan > >> 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. >
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