From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH] KVM: nVMX: Fix setting of CR0 and CR4 in guest mode Date: Mon, 04 Mar 2013 20:37:38 +0100 Message-ID: <5134F802.2020200@web.de> References: <512F270F.1020808@siemens.com> <20130304132234.GP23616@redhat.com> <5134AB2F.20807@siemens.com> <20130304141515.GQ23616@redhat.com> <5134AEEB.9020600@siemens.com> <20130304175632.GD14220@redhat.com> <5134E308.3000202@siemens.com> <20130304183956.GF14220@redhat.com> <5134F4C8.9010807@web.de> <20130304193331.GG14220@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="----enig2AHSKEQSQSSNUGAWQPDNA" Cc: Marcelo Tosatti , kvm , Nadav Har'El , "Nakajima, Jun" To: Gleb Natapov Return-path: Received: from mout.web.de ([212.227.17.11]:58507 "EHLO mout.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758335Ab3CDThv (ORCPT ); Mon, 4 Mar 2013 14:37:51 -0500 In-Reply-To: <20130304193331.GG14220@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 4880 and 3156) ------enig2AHSKEQSQSSNUGAWQPDNA Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 2013-03-04 20:33, Gleb Natapov wrote: > On Mon, Mar 04, 2013 at 08:23:52PM +0100, Jan Kiszka wrote: >> On 2013-03-04 19:39, Gleb Natapov wrote: >>> On Mon, Mar 04, 2013 at 07:08:08PM +0100, Jan Kiszka wrote: >>>> On 2013-03-04 18:56, Gleb Natapov wrote: >>>>> On Mon, Mar 04, 2013 at 03:25:47PM +0100, Jan Kiszka wrote: >>>>>> On 2013-03-04 15:15, Gleb Natapov wrote: >>>>>>> On Mon, Mar 04, 2013 at 03:09:51PM +0100, Jan Kiszka wrote: >>>>>>>> On 2013-03-04 14:22, Gleb Natapov wrote: >>>>>>>>> On Thu, Feb 28, 2013 at 10:44:47AM +0100, Jan Kiszka wrote: >>>>>>>>>> The logic for calculating the value with which we call kvm_set= _cr0/4 was >>>>>>>>>> broken (will definitely be visible with nested unrestricted gu= est mode >>>>>>>>>> support). Also, we performed the check regarding CR0_ALWAYSON = too early >>>>>>>>>> when in guest mode. >>>>>>>>>> >>>>>>>>>> What really needs to be done on both CR0 and CR4 is to mask ou= t L1-owned >>>>>>>>>> bits and merge them in from GUEST_CR0/4. In contrast, arch.cr0= /4 and >>>>>>>>>> arch.cr0/4_guest_owned_bits contain the mangled L0+L1 state an= d, thus, >>>>>>>>>> are not suited as input. >>>>>>>>>> >>>>>>>>>> For both CRs, we can then apply the check against VMXON_CRx_AL= WAYSON and >>>>>>>>>> refuse the update if it fails. To be fully consistent, we impl= ement this >>>>>>>>>> check now also for CR4. >>>>>>>>>> >>>>>>>>>> Finally, we have to set the shadow to the value L2 wanted to w= rite >>>>>>>>>> originally. >>>>>>>>>> >>>>>>>>>> Signed-off-by: Jan Kiszka >>>>>>>>>> --- >>>>>>>>>> >>>>>>>>>> Found while making unrestricted guest mode working. Not sure w= hat impact >>>>>>>>>> the bugs had on current feature level, if any. >>>>>>>>>> >>>>>>>>>> For interested folks, I've pushed my nEPT environment here: >>>>>>>>>> >>>>>>>>>> git://git.kiszka.org/linux-kvm.git nept-hacking >>>>>>>>>> >>>>>>>>>> arch/x86/kvm/vmx.c | 49 ++++++++++++++++++++++++++++++-----= -------------- >>>>>>>>>> 1 files changed, 30 insertions(+), 19 deletions(-) >>>>>>>>>> >>>>>>>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>>>>>>>>> index 7cc566b..d1dac08 100644 >>>>>>>>>> --- a/arch/x86/kvm/vmx.c >>>>>>>>>> +++ b/arch/x86/kvm/vmx.c >>>>>>>>>> @@ -4605,37 +4605,48 @@ vmx_patch_hypercall(struct kvm_vcpu *v= cpu, unsigned char *hypercall) >>>>>>>>>> /* called to set cr0 as appropriate for a mov-to-cr0 exit. */= >>>>>>>>>> static int handle_set_cr0(struct kvm_vcpu *vcpu, unsigned lon= g val) >>>>>>>>>> { >>>>>>>>>> - if (to_vmx(vcpu)->nested.vmxon && >>>>>>>>>> - ((val & VMXON_CR0_ALWAYSON) !=3D VMXON_CR0_ALWAYSON)) >>>>>>>>>> - return 1; >>>>>>>>>> - >>>>>>>>>> if (is_guest_mode(vcpu)) { >>>>>>>>>> - /* >>>>>>>>>> - * We get here when L2 changed cr0 in a way that did not ch= ange >>>>>>>>>> - * any of L1's shadowed bits (see nested_vmx_exit_handled_c= r), >>>>>>>>>> - * but did change L0 shadowed bits. This can currently happ= en >>>>>>>>>> - * with the TS bit: L0 may want to leave TS on (for lazy fp= u >>>>>>>>>> - * loading) while pretending to allow the guest to change i= t. >>>>>>>>>> - */ >>>>>>>>> Can't say I understand this patch yet, but it looks like the co= mment is >>>>>>>>> still valid. Why have you removed it? >>>>>>>> >>>>>>>> L0 allows L1 or L2 at most to own TS, the rest is host-owned. I = think >>>>>>>> the comment was always misleading. >>>>>>>> >>>>>>> I do not see how it is misleading. For everything but TS we will = not get >>>>>>> here (if L1 is kvm). For TS we will get here if L1 allows L2 to c= hange >>>>>>> it, but L0 does not. >>>>>> >>>>>> For everything *but guest-owned* we will get here, thus for most C= R0 >>>>>> accesses (bit-wise, not regarding frequency). >>>>>> >>>>> I do not see how. If bit is trapped by L1 we will not get here. We = will >>>>> do vmexit to L1 instead. nested_vmx_exit_handled_cr() check this co= ndition. >>>>> I am not arguing about you code (didn't grok it yet), but the comme= nt >>>>> still make sense to me. >>>> >>>> "We get here when L2 changed cr0 in a way that did not change any of= >>>> L1's shadowed bits (see nested_vmx_exit_handled_cr), but did change = L0 >>>> shadowed bits." That I can sign. But the rest about TS is just >>>> misleading as we trap _every_ change in L0 - except for TS under cer= tain >>>> conditions. The old code was tested against TS only, that's what the= >>>> comment witness. >>>> >>> TS is just an example of how we can get here with KVM on KVM. Obvious= ly >>> other hypervisors may have different configuration. L2 may allow full= >>> guest access to CR0 and then each CR0 write by L2 will be handled her= e. >>> Under what other condition "we trap _every_ change in L0 - except for= >>> TS" here? >> >> On FPU activation: >> >> cr0_guest_owned_bits =3D X86_CR0_TS; >> >> And on FPU deactivation: >> >> cr0_guest_owned_bits =3D 0; >> > That's exactly TS case that comment explains. Note that > CR0_GUEST_HOST_MASK =3D ~cr0_guest_owned_bits. Again, it's the inverse of what the comment suggest: we enter handle_set_cr0 for every change on CR0 that doesn't match the shadow - except TS was given to the guest by both L1 and L0 (or TS isn't changed as well). >=20 >>> >>>> If you prefer, I'll leave part one in. >>>> >>> Please do so. Without the comment it is not obvious why exit conditio= n >>> is not checked here. Still do not see why you object to TS part. >> >> It describes a corner case in a way that suggests this is the only >> reason why we get here. >> > For KVM on KVM it is. Which is, sorry, irrelevant. Jan ------enig2AHSKEQSQSSNUGAWQPDNA Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAlE0+AIACgkQitSsb3rl5xR0rACg8C3bYR3pM4KtK+lSgeB2bce6 tjIAni837wshwke+LNzwtDUMJqlRL/Vb =3Rxx -----END PGP SIGNATURE----- ------enig2AHSKEQSQSSNUGAWQPDNA--