From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
Wanpeng Li <kernellwp@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH] KVM: vPMU: Don't program counter for interrupt-based event sampling w/o lapic_in_kernel
Date: Mon, 25 Oct 2021 18:44:56 +0200 [thread overview]
Message-ID: <84444ec9-cebf-1ec2-ec3e-8b28e587682d@redhat.com> (raw)
In-Reply-To: <YXbb5ePpVWKxBsbh@google.com>
On 25/10/21 18:31, Sean Christopherson wrote:
>> vPMU depends on in-kernel lapic to deliver pmi interrupt, there is a
>> lot of overhead when creating/maintaining perf_event object,
>> locking/unlocking perf_event_ctx etc for vPMU. It silently fails to
>> deliver pmi interrupt if w/o in-kernel lapic currently. Let's not
>> program counter for interrupt-based event sampling w/o in-kernel
>> lapic support to avoid the whole bothering.
>
> This feels all kinds of wrong. AFAIK, there's no way for KVM to enumerate to
> the guest that the vPMU isn't capable of generating interrupts. I.e. any setup
> that exposes a vPMU to the guest without an in-kernel local APIC is either
> inherently broken or requires a paravirtualized guest. I don't think KVM's bugs
> should be optimized.
Yeah, if it simplified the code it would be a different story, but here
there's even not one but two new checks.
Paolo
prev parent reply other threads:[~2021-10-25 16:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-22 9:17 [PATCH] KVM: vPMU: Don't program counter for interrupt-based event sampling w/o lapic_in_kernel Wanpeng Li
2021-10-25 16:31 ` Sean Christopherson
2021-10-25 16:44 ` Paolo Bonzini [this message]
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