From: Paolo Bonzini <pbonzini@redhat.com>
To: Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc: "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<linux-kernel@vger.kernel.org>, Jim Mattson <jmattson@google.com>,
Joerg Roedel <joro@8bytes.org>, Borislav Petkov <bp@alien8.de>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH v2 0/8] My AVIC patch queue
Date: Mon, 26 Jul 2021 19:24:51 +0200 [thread overview]
Message-ID: <e57ac09d-e697-f917-c19d-26fa74b2af7e@redhat.com> (raw)
In-Reply-To: <20210713142023.106183-1-mlevitsk@redhat.com>
On 13/07/21 16:20, Maxim Levitsky wrote:
> Hi!
>
> This is a series of bugfixes to the AVIC dynamic inhibition, which was
> made while trying to fix bugs as much as possible, in this area and trying
> to make the AVIC+SYNIC conditional enablement work.
>
> * Patches 1-4 address an issue of possible
> mismatch between the AVIC inhibit state and AVIC enable state on all vCPUs.
>
> Since AVICs state is changed via a request there is a window during which
> the states differ which can lead to various warnings and errors.
>
> There was an earlier attempt to fix this by changing the AVIC enable state
> on the current vCPU immediately when the AVIC inhibit request is created,
> however while this fixes the common case, it actually hides the issue deeper,
> because on all other vCPUs but current one, the two states can still
> mismatch till the KVM_REQ_APICV_UPDATE is processed on each of them.
>
> My take on this is to fix the places where the mismatch causes the
> issues instead and then drop the special case of toggling the AVIC right
> away in kvm_request_apicv_update.
>
> V2: I rewrote the commit description for the patch that touches
> avic inhibition in nested case.
>
> * Patches 5-6 in this series fix a race condition which can cause
> a lost write from a guest to APIC when the APIC write races
> the AVIC un-inhibition, and add a warning to catch this problem
> if it re-emerges again.
>
> V2: I re-implemented this with a mutex in V2.
>
> * Patch 7 is an fix yet another issue I found in AVIC inhibit code:
> Currently avic_vcpu_load/avic_vcpu_put are called on userspace entry/exit
> from KVM (aka kvm_vcpu_get/kvm_vcpu_put), and these functions update the
> "is running" bit in the AVIC physical ID remap table and update the
> target vCPU in iommu code.
>
> However both of these functions don't do anything when AVIC is inhibited
> thus the "is running" bit will be kept enabled during exit to userspace.
> This shouldn't be a big issue as the caller
> doesn't use the AVIC when inhibited but still inconsistent and can trigger
> a warning about this in avic_vcpu_load.
>
> To be on the safe side I think it makes sense to call
> avic_vcpu_put/avic_vcpu_load when inhibiting/uninhibiting the AVIC.
> This will ensure that the work these functions do is matched.
>
> * Patch 8 is the patch from Vitaly about allowing AVIC with SYNC
> as long as the guest doesn’t use the AutoEOI feature. I only slightly
> changed it to drop the SRCU lock around call to kvm_request_apicv_update
> and also expose the AutoEOI cpuid bit regardless of AVIC enablement.
>
> Despite the fact that this is the last patch in this series, this patch
> doesn't depend on the other fixes.
>
> Best regards,
> Maxim Levitsky
>
> Maxim Levitsky (7):
> KVM: SVM: svm_set_vintr don't warn if AVIC is active but is about to
> be deactivated
> KVM: SVM: tweak warning about enabled AVIC on nested entry
> KVM: SVM: use vmcb01 in svm_refresh_apicv_exec_ctrl
> KVM: x86: APICv: drop immediate APICv disablement on current vCPU
> KVM: x86: APICv: fix race in kvm_request_apicv_update on SVM
> KVM: SVM: add warning for mistmatch between AVIC state and AVIC access
> page state
> KVM: SVM: call avic_vcpu_load/avic_vcpu_put when enabling/disabling
> AVIC
>
> Vitaly Kuznetsov (1):
> KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in
> use
>
> arch/x86/include/asm/kvm_host.h | 3 ++
> arch/x86/kvm/hyperv.c | 34 ++++++++++++++++----
> arch/x86/kvm/svm/avic.c | 45 ++++++++++++++------------
> arch/x86/kvm/svm/nested.c | 2 +-
> arch/x86/kvm/svm/svm.c | 18 ++++++++---
> arch/x86/kvm/x86.c | 57 ++++++++++++++++++---------------
> include/linux/kvm_host.h | 1 +
> virt/kvm/kvm_main.c | 1 +
> 8 files changed, 103 insertions(+), 58 deletions(-)
>
Queued patches 1-4, thanks.
Paolo
prev parent reply other threads:[~2021-07-26 17:25 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-13 14:20 [PATCH v2 0/8] My AVIC patch queue Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 1/8] KVM: SVM: svm_set_vintr don't warn if AVIC is active but is about to be deactivated Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 2/8] KVM: SVM: tweak warning about enabled AVIC on nested entry Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 3/8] KVM: SVM: use vmcb01 in svm_refresh_apicv_exec_ctrl Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 4/8] KVM: x86: APICv: drop immediate APICv disablement on current vCPU Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 5/8] KVM: x86: APICv: fix race in kvm_request_apicv_update on SVM Maxim Levitsky
2021-07-26 22:34 ` Paolo Bonzini
2021-07-27 13:22 ` Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 6/8] KVM: SVM: add warning for mistmatch between AVIC state and AVIC access page state Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 7/8] KVM: SVM: call avic_vcpu_load/avic_vcpu_put when enabling/disabling AVIC Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 8/8] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use Maxim Levitsky
2021-07-18 12:13 ` Maxim Levitsky
2021-07-19 7:47 ` Vitaly Kuznetsov
2021-07-19 9:00 ` Maxim Levitsky
2021-07-19 9:23 ` Vitaly Kuznetsov
2021-07-19 9:58 ` Maxim Levitsky
2021-07-19 18:49 ` Sean Christopherson
2021-07-20 9:40 ` Maxim Levitsky
2021-07-22 9:12 ` KVM's support for non default APIC base Maxim Levitsky
2021-08-02 9:20 ` Maxim Levitsky
2021-08-06 21:55 ` Sean Christopherson
2021-08-09 9:40 ` Maxim Levitsky
2021-08-09 15:57 ` Sean Christopherson
2021-08-09 16:47 ` Jim Mattson
2021-08-10 20:42 ` Maxim Levitsky
2021-07-22 17:35 ` [PATCH v2 8/8] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use Maxim Levitsky
2021-07-22 19:06 ` Sean Christopherson
2021-07-27 13:05 ` Maxim Levitsky
2021-07-27 17:48 ` Ben Gardon
2021-07-27 18:17 ` Sean Christopherson
2021-07-29 14:10 ` Maxim Levitsky
2021-07-26 17:24 ` Paolo Bonzini [this message]
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