From: Maxim Levitsky <mlevitsk@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Li RongQing <lirongqing@baidu.com>
Subject: Re: [PATCH 17/19] KVM: SVM: Handle multiple logical targets in AVIC kick fastpath
Date: Wed, 31 Aug 2022 21:25:00 +0300 [thread overview]
Message-ID: <d15e7d7e922b615fbc701ce766caa3e8c703bc6f.camel@redhat.com> (raw)
In-Reply-To: <Yw+mFbuih3rBjMV8@google.com>
On Wed, 2022-08-31 at 18:19 +0000, Sean Christopherson wrote:
> On Wed, Aug 31, 2022, Maxim Levitsky wrote:
> > On Wed, 2022-08-31 at 00:35 +0000, Sean Christopherson wrote:
> > > +static void avic_kick_vcpu_by_logical_id(struct kvm *kvm, u32 *avic_logical_id_table,
> > > + u32 logid_index, u32 icrl)
> > > +{
> > > + u32 physical_id;
> > > +
> > > + if (!avic_logical_id_table) {
> > ^ Typo, the '!' shoudn't be there.
>
> Ouch. I suspect the tests pass because this just ends up routing events through
> the slow path. I try to concoct a testcase to expose this bug.
>
> > > +static bool is_optimized_logical_map_enabled(struct kvm *kvm)
> > > +{
> > > + struct kvm_apic_map *map;
> > > + bool enabled;
> > > +
> > > + rcu_read_lock();
> > > + map = rcu_dereference(kvm->arch.apic_map);
> > > + enabled = map && map->logical_mode != KVM_APIC_MODE_MAP_DISABLED;
> > > + rcu_read_unlock();
> > > + return enabled;
> > > +}
> >
> > This function doesn't belong to avic, it should be in common KVM code.
>
> I'll move it. I'm not expecting any additional users, but I agree it belongs
> elsewhere. Actually, might be a moot point (see below).
>
> > > @@ -394,50 +449,27 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source
> > > if (unlikely(!bitmap))
> > > return 0;
> > >
> > > - if (!is_power_of_2(bitmap))
> > > - /* multiple logical destinations, use slow path */
> > > + /*
> > > + * Use the slow path if more than one bit is set in the bitmap
> > > + * and KVM's optimized logical map is disabled to avoid kicking
> > > + * a vCPU multiple times. If the optimized map is disabled, a
> > > + * vCPU _may_ have multiple bits set in its logical ID, i.e.
> > > + * may have multiple entries in the logical table.
> > > + */
> > > + if (!is_power_of_2(bitmap) &&
> > > + !is_optimized_logical_map_enabled(kvm))
> > > return -EINVAL;
> >
> > I hate to say it but there is another issue here, which I know about for a while
> > but haven't gotten yet to fix.
> >
> > The issue is that AVIC's logical to physical map can't cover all the corner cases
> > that you discovered - it only supports the sane subset: for each cluster, and for each bit
> > in the mask, it has a physical apic id - so things like logical ids with multiple bits,
> > having same logical id for multiple vcpus and so on can't work.
> >
> > In this case we need to either inhibit AVIC (I support this 100%),
>
> I like the idea of inhibiting.
>
> > or clear its logical ID map, so all logicical IPIs VM exit, and then they
> > can be emulated.
> >
> > I haven't studied it formally but the code which rebuilds the AVIC's logical ID map
> > starts at 'avic_handle_ldr_update'.
>
> I suspected there are issues here, but the new tests passed (somewhat surprisingly)
> so I stopped trying to decipher the AVIC LDR handling.
>
> Eww. And the VM-Exit trap logic is broken too. If the guest updates and disables
> its LDR, SVM returns immediately and doesn't call into common APIC code, i.e. doesn't
> recalc the optimized map. E.g. if the guest clears its LDR, the optimized map will
> be left as is and the vCPU will receive interrupts using its old LDR.
>
> case APIC_LDR:
> if (avic_handle_ldr_update(vcpu))
> return 0;
> break;
>
> Rather than handling this purely in AVIC code, what if we a key off of
> the optimized map being enabled? E.g. drop the return from avic_handle_ldr_update()
> and in the kvm_recalculate_apic_map() do:
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 3b6ef36b3963..6e188010b614 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -364,6 +364,11 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
> cluster[ldr] = apic;
> }
> out:
> + if (!new || new->logical_mode == KVM_APIC_MODE_MAP_DISABLED)
> + kvm_set_apicv_inhibit(kvm, APICV_INHIBIT_REASON_LOGICAL_MAP_DISABLED);
> + else
> + kvm_clear_apicv_inhibit(kvm, APICV_INHIBIT_REASON_LOGICAL_MAP_DISABLED);
> +
This looks very good, it will even work on APICv, because the 'check_apicv_inhibit_reasons'
will not return true for this new reason (APICv IPIv I think doesn't deal with logical destination at all);
Best regards,
Maxim Levitsky
> old = rcu_dereference_protected(kvm->arch.apic_map,
> lockdep_is_held(&kvm->arch.apic_map_lock));
> rcu_assign_pointer(kvm->arch.apic_map, new);
>
next prev parent reply other threads:[~2022-08-31 18:30 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-31 0:34 [PATCH 00/19] KVM: x86: AVIC and local APIC fixes+cleanups Sean Christopherson
2022-08-31 0:34 ` [PATCH 01/19] KVM: SVM: Process ICR on AVIC IPI delivery failure due to invalid target Sean Christopherson
2022-08-31 9:18 ` Maxim Levitsky
2022-08-31 0:34 ` [PATCH 02/19] KVM: SVM: Don't put/load AVIC when setting virtual APIC mode Sean Christopherson
2022-08-31 9:24 ` Maxim Levitsky
2022-08-31 16:33 ` Sean Christopherson
2022-08-31 0:34 ` [PATCH 03/19] Revert "KVM: SVM: Introduce hybrid-AVIC mode" Sean Christopherson
2022-08-31 5:59 ` Maxim Levitsky
2022-08-31 6:45 ` Maxim Levitsky
2022-08-31 16:29 ` Sean Christopherson
2022-08-31 17:46 ` Maxim Levitsky
2022-08-31 17:58 ` Jim Mattson
2022-08-31 18:01 ` Maxim Levitsky
2022-08-31 19:12 ` Sean Christopherson
2022-09-01 10:25 ` Maxim Levitsky
2022-09-01 11:47 ` Jim Mattson
2022-09-01 13:29 ` Sean Christopherson
2022-09-01 13:53 ` Sean Christopherson
2022-09-01 15:08 ` Sean Christopherson
2022-08-31 16:19 ` Sean Christopherson
2022-08-31 17:47 ` Maxim Levitsky
2022-08-31 0:34 ` [PATCH 04/19] KVM: SVM: Replace "avic_mode" enum with "x2avic_enabled" boolean Sean Christopherson
2022-08-31 9:36 ` Maxim Levitsky
2022-08-31 0:34 ` [PATCH 05/19] KVM: SVM: Compute dest based on sender's x2APIC status for AVIC kick Sean Christopherson
2022-08-31 9:38 ` Maxim Levitsky
2022-09-01 2:56 ` Li,Rongqing
2022-08-31 0:34 ` [PATCH 06/19] KVM: SVM: Get x2APIC logical dest bitmap from ICRH[15:0], not ICHR[31:16] Sean Christopherson
2022-08-31 6:09 ` Maxim Levitsky
2022-08-31 9:43 ` Maxim Levitsky
2022-08-31 16:35 ` Sean Christopherson
2022-08-31 18:18 ` Maxim Levitsky
2022-08-31 0:34 ` [PATCH 07/19] KVM: SVM: Drop buggy and redundant AVIC "single logical dest" check Sean Christopherson
2022-08-31 6:19 ` Maxim Levitsky
2022-08-31 16:37 ` Sean Christopherson
2022-08-31 18:10 ` Maxim Levitsky
2022-08-31 0:34 ` [PATCH 08/19] KVM: SVM: Remove redundant cluster calculation that also creates a shadow Sean Christopherson
2022-08-31 10:19 ` Maxim Levitsky
2022-09-01 20:02 ` Sean Christopherson
2022-08-31 0:34 ` [PATCH 09/19] KVM: SVM: Drop duplicate calcuation of AVIC/x2AVIC "logical index" Sean Christopherson
2022-08-31 0:34 ` [PATCH 10/19] KVM: SVM: Document that vCPU ID == APIC ID in AVIC kick fastpatch Sean Christopherson
2022-08-31 10:22 ` Maxim Levitsky
2022-08-31 16:16 ` Sean Christopherson
2022-08-31 17:49 ` Maxim Levitsky
2022-08-31 0:34 ` [PATCH 11/19] KVM: SVM: Add helper to perform final AVIC "kick" of single vCPU Sean Christopherson
2022-08-31 10:25 ` Maxim Levitsky
2022-08-31 15:08 ` Sean Christopherson
2022-08-31 18:12 ` Maxim Levitsky
2022-08-31 0:34 ` [PATCH 12/19] KVM: x86: Disable APIC logical map if logical ID covers multiple MDAs Sean Christopherson
2022-08-31 13:23 ` Maxim Levitsky
2022-08-31 0:35 ` [PATCH 13/19] KVM: x86: Disable APIC logical map if vCPUs are aliased in logical mode Sean Christopherson
2022-08-31 13:24 ` Maxim Levitsky
2022-08-31 0:35 ` [PATCH 14/19] KVM: x86: Honor architectural behavior for aliased 8-bit APIC IDs Sean Christopherson
2022-08-31 13:37 ` Maxim Levitsky
2022-08-31 16:41 ` Sean Christopherson
2022-08-31 17:51 ` Maxim Levitsky
2022-08-31 0:35 ` [PATCH 15/19] KVM: x86: Explicitly skip optimized logical map setup if vCPU's LDR==0 Sean Christopherson
2022-08-31 13:41 ` Maxim Levitsky
2022-08-31 16:47 ` Sean Christopherson
2022-08-31 0:35 ` [PATCH 16/19] KVM: x86: Explicitly track all possibilities for APIC map's logical modes Sean Christopherson
2022-08-31 13:43 ` Maxim Levitsky
2022-08-31 16:56 ` Sean Christopherson
2022-08-31 17:53 ` Maxim Levitsky
2022-09-16 18:58 ` Sean Christopherson
2022-08-31 18:42 ` Maxim Levitsky
2022-08-31 19:17 ` Sean Christopherson
2022-08-31 0:35 ` [PATCH 17/19] KVM: SVM: Handle multiple logical targets in AVIC kick fastpath Sean Christopherson
2022-08-31 13:57 ` Maxim Levitsky
2022-08-31 18:19 ` Sean Christopherson
2022-08-31 18:25 ` Maxim Levitsky [this message]
2022-08-31 0:35 ` [PATCH 18/19] KVM: SVM: Ignore writes to Remote Read Data on AVIC write traps Sean Christopherson
2022-08-31 10:40 ` Maxim Levitsky
2022-08-31 0:35 ` [PATCH 19/19] Revert "KVM: SVM: Do not throw warning when calling avic_vcpu_load on a running vcpu" Sean Christopherson
2022-08-31 6:07 ` Maxim Levitsky
2022-08-31 7:03 ` Maxim Levitsky
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=d15e7d7e922b615fbc701ce766caa3e8c703bc6f.camel@redhat.com \
--to=mlevitsk@redhat.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=lirongqing@baidu.com \
--cc=pbonzini@redhat.com \
--cc=seanjc@google.com \
--cc=suravee.suthikulpanit@amd.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).