From: Sean Christopherson <seanjc@google.com>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Alejandro Jimenez <alejandro.j.jimenez@oracle.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Li RongQing <lirongqing@baidu.com>
Subject: Re: [PATCH v3 07/28] KVM: x86: Inhibit APIC memslot if x2APIC and AVIC are enabled
Date: Wed, 28 Sep 2022 22:35:31 +0000 [thread overview]
Message-ID: <YzTMM+bYVSNmEatL@google.com> (raw)
In-Reply-To: <2ca1b7c59e2abe661dd03309ad13eca7d692ff05.camel@redhat.com>
On Wed, Sep 28, 2022, Maxim Levitsky wrote:
> On Wed, 2022-09-28 at 16:33 +0000, Sean Christopherson wrote:
> > Similarly, is there a good reason for having nested_svm_vmexit() invoke
> > kvm_vcpu_update_apicv() directly? I'm confused by the "so that other vCPUs can
> > start to benefit from it right away". The nested inhibit is per-vCPU and so
> > should only affect the current vCPU, no? I.e. for all intents and purposes, using
> > a request should be functionally equivalent.
>
> It is kind of the other way around:
>
> The mere fact of switching to vmcb02 *inhibits* the AVIC on the current vCPU,
> but the AVIC inhibit is there only to set the is_running bits in the physid table
> and in IOMMU to prevent its *peers* to try and send interrupts to it via AVIC.
>
> It is the reason why APICv doesn't need it - the posted interrupts still work
> just fine when a vCPU doens't use APICv, or uses a different posted interrupt vector
> when it uses the nested APICv.
Gotcha, the "other vCPUs" part is where I got confused.
> So it makes sense to remove that inhibit as soon as possible that the peers
> could stop getting 'unaccellerated IPI' vmexits for nothing.
But practically speaking, the delay between the nested VM-Exit and servicing the
request is minimal. Might be a moot point if nested AVIC is supported, i.e. an
inline update may be "required" at that point.
Not a sticking point by any means, but if possible, it would be nice to have a
single call site for the per-vCPU APICv update.
> However back to the discussion, I don't think this is a problem.
>
> We can just call both the kvm_vcpu_update_apicv() and a new function that
> does the memslot disable from KVM_REQ_APICV_UPDATE, then
> plain kvm_vcpu_update_apicv() won't need to drop the srcu lock.
>
> It is pretty much the same that you proposed, just instead of piggybacking on
> KVM_REQ_UNBLOCK, I proposed to piggyback on KVM_REQ_APICV_UPDATE.
Yep, easy to do after converting the x2APIC toggling to use a request.
Thanks!
next prev parent reply other threads:[~2022-09-28 22:36 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-20 23:31 [PATCH v3 00/28] KVM: x86: AVIC and local APIC fixes+cleanups Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 01/28] KVM: x86: Blindly get current x2APIC reg value on "nodecode write" traps Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 02/28] KVM: x86: Purge "highest ISR" cache when updating APICv state Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 03/28] KVM: SVM: Flush the "current" TLB when activating AVIC Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 04/28] KVM: SVM: Process ICR on AVIC IPI delivery failure due to invalid target Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 05/28] KVM: x86: Don't inhibit APICv/AVIC if xAPIC ID mismatch is due to 32-bit ID Sean Christopherson
2022-09-28 3:15 ` Alejandro Jimenez
2022-09-28 5:55 ` Maxim Levitsky
2022-09-28 16:51 ` Sean Christopherson
2022-09-28 17:51 ` Maxim Levitsky
2022-09-28 18:03 ` Sean Christopherson
2022-09-28 18:16 ` Maxim Levitsky
2022-09-28 20:44 ` Sean Christopherson
2022-09-28 20:50 ` Alejandro Jimenez
2022-09-20 23:31 ` [PATCH v3 06/28] KVM: x86: Move APIC access page helper to common x86 code Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 07/28] KVM: x86: Inhibit APIC memslot if x2APIC and AVIC are enabled Sean Christopherson
2022-09-23 10:27 ` Maxim Levitsky
2022-09-26 17:00 ` Sean Christopherson
2022-09-28 6:21 ` Maxim Levitsky
2022-09-28 16:33 ` Sean Christopherson
2022-09-28 17:40 ` Maxim Levitsky
2022-09-28 22:35 ` Sean Christopherson [this message]
2022-09-20 23:31 ` [PATCH v3 08/28] KVM: SVM: Don't put/load AVIC when setting virtual APIC mode Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 09/28] KVM: SVM: Replace "avic_mode" enum with "x2avic_enabled" boolean Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 10/28] KVM: SVM: Compute dest based on sender's x2APIC status for AVIC kick Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 11/28] KVM: SVM: Fix x2APIC Logical ID calculation for avic_kick_target_vcpus_fast Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 12/28] Revert "KVM: SVM: Use target APIC ID to complete x2AVIC IRQs when possible" Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 13/28] KVM: SVM: Document that vCPU ID == APIC ID in AVIC kick fastpatch Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 14/28] KVM: SVM: Add helper to perform final AVIC "kick" of single vCPU Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 15/28] KVM: x86: Explicitly skip optimized logical map setup if vCPU's LDR==0 Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 16/28] KVM: x86: Explicitly track all possibilities for APIC map's logical modes Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 17/28] KVM: x86: Skip redundant x2APIC logical mode optimized cluster setup Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 18/28] KVM: x86: Disable APIC logical map if logical ID covers multiple MDAs Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 19/28] KVM: x86: Disable APIC logical map if vCPUs are aliased in logical mode Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 20/28] KVM: x86: Honor architectural behavior for aliased 8-bit APIC IDs Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 21/28] KVM: x86: Inhibit APICv/AVIC if the optimized physical map is disabled Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 22/28] KVM: SVM: Inhibit AVIC if vCPUs are aliased in logical mode Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 23/28] KVM: SVM: Always update local APIC on writes to logical dest register Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 24/28] KVM: SVM: Update svm->ldr_reg cache even if LDR is "bad" Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 25/28] KVM: SVM: Require logical ID to be power-of-2 for AVIC entry Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 26/28] KVM: SVM: Handle multiple logical targets in AVIC kick fastpath Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 27/28] KVM: SVM: Ignore writes to Remote Read Data on AVIC write traps Sean Christopherson
2022-09-20 23:31 ` [PATCH v3 28/28] Revert "KVM: SVM: Do not throw warning when calling avic_vcpu_load on a running vcpu" Sean Christopherson
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