From: Andy Lutomirski <luto@kernel.org>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: X86 ML <x86@kernel.org>, kvm list <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>
Subject: Re: [PATCH RFC 4/6] KVM: x86: acknowledgment mechanism for async pf page ready notifications
Date: Wed, 29 Apr 2020 10:28:11 -0700 [thread overview]
Message-ID: <CALCETrXEzpKNhNJQm+SshiEfyHjYkB7+1c+7iusZy66rRsWunA@mail.gmail.com> (raw)
In-Reply-To: <20200429093634.1514902-5-vkuznets@redhat.com>
On Wed, Apr 29, 2020 at 2:36 AM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> If two page ready notifications happen back to back the second one is not
> delivered and the only mechanism we currently have is
> kvm_check_async_pf_completion() check in vcpu_run() loop. The check will
> only be performed with the next vmexit when it happens and in some cases
> it may take a while. With interrupt based page ready notification delivery
> the situation is even worse: unlike exceptions, interrupts are not handled
> immediately so we must check if the slot is empty. This is slow and
> unnecessary. Introduce dedicated MSR_KVM_ASYNC_PF_ACK MSR to communicate
> the fact that the slot is free and host should check its notification
> queue. Mandate using it for interrupt based type 2 APF event delivery.
This seems functional, but I'm wondering if it could a bit simpler and
more efficient if the data structure was a normal descriptor ring with
the same number slots as whatever the maximum number of waiting pages
is. Then there would never need to be any notification from the guest
back to the host, since there would always be room for a notification.
It might be even better if a single unified data structure was used
for both notifications.
next prev parent reply other threads:[~2020-04-29 17:28 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-29 9:36 [PATCH RFC 0/6] KVM: x86: Interrupt-based mechanism for async_pf 'page present' notifications Vitaly Kuznetsov
2020-04-29 9:36 ` [PATCH RFC 1/6] Revert "KVM: async_pf: Fix #DF due to inject "Page not Present" and "Page Ready" exceptions simultaneously" Vitaly Kuznetsov
2020-05-05 1:22 ` Gavin Shan
2020-05-05 14:16 ` Vivek Goyal
2020-05-06 15:17 ` Vitaly Kuznetsov
2020-05-11 19:17 ` Vivek Goyal
2020-04-29 9:36 ` [PATCH RFC 2/6] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info Vitaly Kuznetsov
2020-05-04 23:52 ` Gavin Shan
2020-05-05 8:08 ` Vitaly Kuznetsov
2020-04-29 9:36 ` [PATCH RFC 3/6] KVM: x86: interrupt based APF page-ready event delivery Vitaly Kuznetsov
2020-04-29 10:54 ` Paolo Bonzini
2020-04-29 12:40 ` Vitaly Kuznetsov
2020-04-29 13:21 ` Paolo Bonzini
2020-04-29 21:27 ` Peter Xu
2020-04-30 8:31 ` Vitaly Kuznetsov
2020-04-30 13:28 ` Peter Xu
2020-04-30 13:49 ` Vitaly Kuznetsov
2020-05-05 15:22 ` Vivek Goyal
2020-04-29 9:36 ` [PATCH RFC 4/6] KVM: x86: acknowledgment mechanism for async pf page ready notifications Vitaly Kuznetsov
2020-04-29 17:28 ` Andy Lutomirski [this message]
2020-04-29 17:40 ` Paolo Bonzini
2020-04-30 0:45 ` Andy Lutomirski
2020-04-30 6:46 ` Paolo Bonzini
2020-04-30 6:49 ` Paolo Bonzini
2020-04-30 8:40 ` Vitaly Kuznetsov
2020-04-30 9:27 ` Paolo Bonzini
2020-04-30 11:33 ` Vitaly Kuznetsov
2020-04-30 11:43 ` Paolo Bonzini
2020-05-05 0:36 ` Gavin Shan
2020-05-05 8:16 ` Vitaly Kuznetsov
2020-05-05 8:51 ` Gavin Shan
2020-05-05 9:54 ` Paolo Bonzini
2020-04-29 9:36 ` [PATCH RFC 5/6] KVM: x86: announce KVM_FEATURE_ASYNC_PF_INT Vitaly Kuznetsov
2020-04-29 10:40 ` Peter Zijlstra
2020-04-29 9:36 ` [PATCH RFC 6/6] KVM: x86: Switch KVM guest to using interrupts for page ready APF delivery Vitaly Kuznetsov
2020-04-29 10:53 ` Paolo Bonzini
2020-04-29 12:44 ` Vitaly Kuznetsov
2020-04-29 13:19 ` Paolo Bonzini
2020-04-29 14:34 ` Vitaly Kuznetsov
2020-05-05 18:59 ` Vivek Goyal
2020-05-05 0:42 ` Gavin Shan
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