From: Maxim Levitsky <mlevitsk@redhat.com>
To: Chao Gao <chao.gao@intel.com>
Cc: Wanpeng Li <wanpengli@tencent.com>,
kvm@vger.kernel.org, David Airlie <airlied@linux.ie>,
Dave Hansen <dave.hansen@linux.intel.com>,
dri-devel@lists.freedesktop.org, "H. Peter Anvin" <hpa@zytor.com>,
Brijesh Singh <brijesh.singh@amd.com>,
Joerg Roedel <joro@8bytes.org>,
x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
Zhi Wang <zhi.a.wang@intel.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
intel-gfx@lists.freedesktop.org, Borislav Petkov <bp@alien8.de>,
Rodrigo Vivi <rodrigo.vivi@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
intel-gvt-dev@lists.freedesktop.org,
Jim Mattson <jmattson@google.com>,
Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
Sean Christopherson <seanjc@google.com>,
linux-kernel@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [RFC PATCH v3 02/19] KVM: x86: inhibit APICv/AVIC when the guest and/or host changes apic id/base from the defaults.
Date: Wed, 18 May 2022 15:36:44 +0300 [thread overview]
Message-ID: <670fdf36585b1bf7c367cff4ab0653f4c7de8808.camel@redhat.com> (raw)
In-Reply-To: <20220518115056.GA18087@gao-cwp>
On Wed, 2022-05-18 at 19:51 +0800, Chao Gao wrote:
> On Wed, May 18, 2022 at 12:50:27PM +0300, Maxim Levitsky wrote:
> > > > struct kvm_arch {
> > > > @@ -1258,6 +1260,7 @@ struct kvm_arch {
> > > > hpa_t hv_root_tdp;
> > > > spinlock_t hv_root_tdp_lock;
> > > > #endif
> > > > + bool apic_id_changed;
> > >
> > > What's the value of this boolean? No one reads it.
> >
> > I use it in later patches to kill the guest during nested VM entry
> > if it attempts to use nested AVIC after any vCPU changed APIC ID.
> >
> > I mentioned this boolean in the commit description.
> >
> > This boolean avoids the need to go over all vCPUs and checking
> > if they still have the initial apic id.
>
> Do you want to kill the guest if APIC base got changed? If yes,
> you can check if APICV_INHIBIT_REASON_RO_SETTINGS is set and save
> the boolean.
Yep, I thrown in the apic base just because I can. It doesn't matter to
my nested AVIC logic at all, but since it is also something that guests
don't change, I also don't care if this will lead to inhibit and
killing the guest if it attempts to use nested AVIC.
That boolean should have the same value as the APICV_INHIBIT_REASON_RO_SETTINGS
inhibit, so yes I can instead check if the inhibit is active.
I don't know if that is cleaner that this boolean though, individual
inhibit value is currently not something that anybody uses in logic.
Best regards,
Maxim Levitsky
>
> > In the future maybe we can introduce a more generic 'taint'
> > bitmap with various flags like that, indicating that the guest
> > did something unexpected.
> >
> > BTW, the other option in regard to the nested AVIC is just to ignore this issue completely.
> > The code itself always uses vcpu_id's, thus regardless of when/how often the guest changes
> > its apic ids, my code would just use the initial APIC ID values consistently.
> >
> > In this case I won't need this boolean.
> >
> > > > };
> > > >
> > > > struct kvm_vm_stat {
> > > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > > > index 66b0eb0bda94e..8996675b3ef4c 100644
> > > > --- a/arch/x86/kvm/lapic.c
> > > > +++ b/arch/x86/kvm/lapic.c
> > > > @@ -2038,6 +2038,19 @@ static void apic_manage_nmi_watchdog(struct kvm_lapic *apic, u32 lvt0_val)
> > > > }
> > > > }
> > > >
> > > > +static void kvm_lapic_check_initial_apic_id(struct kvm_lapic *apic)
> > > > +{
> > > > + if (kvm_apic_has_initial_apic_id(apic))
> > > > + return;
> > > > +
> > > > + pr_warn_once("APIC ID change is unsupported by KVM");
> > >
> > > It is misleading because changing xAPIC ID is supported by KVM; it just
> > > isn't compatible with APICv. Probably this pr_warn_once() should be
> > > removed.
> >
> > Honestly since nobody uses this feature, I am not sure if to call this supported,
> > I am sure that KVM has more bugs in regard of using non standard APIC ID.
> > This warning might hopefuly make someone complain about it if this
> > feature is actually used somewhere.
>
> Now I got you. It is fine to me.
>
next prev parent reply other threads:[~2022-05-18 12:37 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-27 20:02 [RFC PATCH v3 00/19] RFC: nested AVIC Maxim Levitsky
2022-04-27 20:02 ` [RFC PATCH v3 01/19] KVM: x86: document AVIC/APICv inhibit reasons Maxim Levitsky
2022-05-18 15:56 ` Sean Christopherson
2022-05-18 17:13 ` Maxim Levitsky
2022-04-27 20:02 ` [RFC PATCH v3 02/19] KVM: x86: inhibit APICv/AVIC when the guest and/or host changes apic id/base from the defaults Maxim Levitsky
2022-05-18 8:28 ` Chao Gao
2022-05-18 9:50 ` Maxim Levitsky
2022-05-18 11:51 ` Chao Gao
2022-05-18 12:36 ` Maxim Levitsky [this message]
2022-05-18 15:39 ` Sean Christopherson
2022-05-18 17:15 ` Maxim Levitsky
2022-05-19 16:06 ` Sean Christopherson
2022-05-22 9:03 ` Maxim Levitsky
2022-05-22 14:47 ` Jim Mattson
2022-05-23 6:50 ` Maxim Levitsky
2022-05-23 17:22 ` Jim Mattson
2022-05-23 17:31 ` Sean Christopherson
2022-06-23 9:44 ` Maxim Levitsky
2022-04-27 20:02 ` [RFC PATCH v3 03/19] KVM: x86: SVM: remove avic's broken code that updated APIC ID Maxim Levitsky
2022-05-19 16:10 ` Sean Christopherson
2022-05-22 9:01 ` Maxim Levitsky
2022-05-23 17:19 ` Sean Christopherson
2022-04-27 20:02 ` [RFC PATCH v3 04/19] KVM: x86: mmu: allow to enable write tracking externally Maxim Levitsky
2022-05-19 16:27 ` Sean Christopherson
2022-05-22 10:21 ` Maxim Levitsky
2022-05-19 16:37 ` Sean Christopherson
2022-05-22 10:22 ` Maxim Levitsky
2022-07-20 14:42 ` Maxim Levitsky
2022-07-25 16:08 ` Sean Christopherson
2022-07-28 7:46 ` Maxim Levitsky
2022-08-01 15:53 ` Maxim Levitsky
2022-08-01 17:20 ` Sean Christopherson
2022-08-08 13:13 ` Nested AVIC design (was:Re: [RFC PATCH v3 04/19] KVM: x86: mmu: allow to enable write tracking externally) Maxim Levitsky
2022-09-29 22:38 ` Sean Christopherson
2022-10-03 7:27 ` Maxim Levitsky
2022-11-10 0:47 ` Sean Christopherson
2022-04-27 20:03 ` [RFC PATCH v3 05/19] x86: KVMGT: use kvm_page_track_write_tracking_enable Maxim Levitsky
2022-05-19 16:38 ` Sean Christopherson
2022-04-27 20:03 ` [RFC PATCH v3 06/19] KVM: x86: mmu: add gfn_in_memslot helper Maxim Levitsky
2022-05-19 16:43 ` Sean Christopherson
2022-05-22 10:22 ` Maxim Levitsky
2022-05-22 12:12 ` Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 07/19] KVM: x86: mmu: tweak fast path for emulation of access to nested NPT pages Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 08/19] KVM: x86: SVM: move avic state to separate struct Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 09/19] KVM: x86: nSVM: add nested AVIC tracepoints Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 10/19] KVM: x86: nSVM: implement AVIC's physid/logid table access helpers Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 11/19] KVM: x86: nSVM: implement shadowing of AVIC's physical id table Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 12/19] KVM: x86: nSVM: make nested AVIC physid write tracking be aware of the host scheduling Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 13/19] KVM: x86: nSVM: wire nested AVIC to nested guest entry/exit Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 14/19] KVM: x86: rename .set_apic_access_page_addr to reload_apic_access_page Maxim Levitsky
2022-05-19 16:55 ` Sean Christopherson
2022-05-22 10:22 ` Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 15/19] KVM: x86: nSVM: add code to reload AVIC physid table when it is invalidated Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 16/19] KVM: x86: nSVM: implement support for nested AVIC vmexits Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 17/19] KVM: x86: nSVM: implement nested AVIC doorbell emulation Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 18/19] KVM: x86: SVM/nSVM: add optional non strict AVIC doorbell mode Maxim Levitsky
2022-04-27 20:03 ` [RFC PATCH v3 19/19] KVM: x86: nSVM: expose the nested AVIC to the guest Maxim Levitsky
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