From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kashyap Chamarthy Subject: Re: [PATCH] KVM: nVMX: mask unrestricted_guest if disabled on L0 Date: Wed, 25 Feb 2015 16:50:32 +0100 Message-ID: <20150225155032.GC30296@tesla.redhat.com> References: <20150219211011.GE28728@tesla.redhat.com> <20150219222832.GA22611@tesla.redhat.com> <20150220161415.GA22152@potion.brq.redhat.com> <20150220194509.GD30563@tesla.home> <20150222154622.GA30296@tesla.redhat.com> <20150223135611.GB2102@potion.brq.redhat.com> <20150223161437.GI30296@tesla.redhat.com> <20150223170906.GA1055@tesla.redhat.com> <20150223180527.GK30296@tesla.redhat.com> <20150224163005.GB2186@potion.brq.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Paolo Bonzini , Jan Kiszka , kvm@vger.kernel.org, dgilbert@redhat.com, bsd@redhat.com, mtosatti@redhat.com To: Radim =?utf-8?B?S3LEjW3DocWZ?= Return-path: Received: from mx1.redhat.com ([209.132.183.28]:45542 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752440AbbBYPuo (ORCPT ); Wed, 25 Feb 2015 10:50:44 -0500 Content-Disposition: inline In-Reply-To: <20150224163005.GB2186@potion.brq.redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Feb 24, 2015 at 05:30:06PM +0100, Radim Kr=C4=8Dm=C3=A1=C5=99 w= rote: > 2015-02-23 19:05+0100, Kashyap Chamarthy: > > Tested with the _correct_ Kernel[1] (that has Radim's patch) now -- > > applied it on both L0 and L1. > >=20 > > Result: Same as before -- Booting L2 causes L1 to reboot. However, = the > > stack trace from `dmesg` on L0 is took slightly different p= ath than > > before -- it's using MSR handling: >=20 > Thanks, the problem was deeper ... L1 enabled unrestricted mode while= L0 > had it disabled. L1 could then vmrun a L2 state that L0 would have t= o > emulate, but that doesn't work. There are at least these solutions: >=20 > 1) don't expose unrestricted_guest when L0 doesn't have it > 2) fix unrestricted mode emulation code > 3) handle the failure a without killing L1 >=20 > I'd do just (1) -- emulating unrestricted mode is a loss. >=20 > I have done initial testing and at least qemu-sanity-check works now: >=20 > ---8<--- > If EPT was enabled, unrestricted_guest was allowed in L1 regardless o= f > L0. L1 triple faulted when running L2 guest that required emulation. >=20 > Another side effect was 'WARN_ON_ONCE(vmx->nested.nested_run_pending)= ' > in L0's dmesg: > WARNING: CPU: 0 PID: 0 at arch/x86/kvm/vmx.c:9190 nested_vmx_vmexit= +0x96e/0xb00 [kvm_intel] () >=20 > Prevent this scenario by masking SECONDARY_EXEC_UNRESTRICTED_GUEST wh= en > the host doesn't have it enabled. >=20 > Fixes: 78051e3b7e35 ("KVM: nVMX: Disable unrestricted mode if ept=3D0= ") > Signed-off-by: Radim Kr=C4=8Dm=C3=A1=C5=99 I just built[1] a Kernel with this patch and tested it on L0 and L1 and can confirm, the patch fixes the issue -- Booting L2 does not cause L1 to reboot. So: Tested-By: Kashyap Chamarthy Thanks for investigating, Radim! [1] https://kashyapc.fedorapeople.org/kernel-4.0.0-0.rc1.git1.1.kashyap= 1.fc23-with-nvmx-fix2-radim/ > --- > arch/x86/kvm/vmx.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) >=20 > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index f7b20b417a3a..dbabea21357b 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -2476,8 +2476,7 @@ static void nested_vmx_setup_ctls_msrs(struct v= cpu_vmx *vmx) > if (enable_ept) { > /* nested EPT: emulate EPT also to L1 */ > vmx->nested.nested_vmx_secondary_ctls_high |=3D > - SECONDARY_EXEC_ENABLE_EPT | > - SECONDARY_EXEC_UNRESTRICTED_GUEST; > + SECONDARY_EXEC_ENABLE_EPT; > vmx->nested.nested_vmx_ept_caps =3D VMX_EPT_PAGE_WALK_4_BIT | > VMX_EPTP_WB_BIT | VMX_EPT_2MB_PAGE_BIT | > VMX_EPT_INVEPT_BIT; > @@ -2491,6 +2490,10 @@ static void nested_vmx_setup_ctls_msrs(struct = vcpu_vmx *vmx) > } else > vmx->nested.nested_vmx_ept_caps =3D 0; > =20 > + if (enable_unrestricted_guest) > + vmx->nested.nested_vmx_secondary_ctls_high |=3D > + SECONDARY_EXEC_UNRESTRICTED_GUEST; > + > /* miscellaneous data */ > rdmsr(MSR_IA32_VMX_MISC, > vmx->nested.nested_vmx_misc_low, --=20 /kashyap