From: Paolo Bonzini <pbonzini@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>,
x86@kernel.org, kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, 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: Thu, 30 Apr 2020 13:43:13 +0200 [thread overview]
Message-ID: <0ff17250-1943-837a-734d-73a8b4a97ae2@redhat.com> (raw)
In-Reply-To: <87k11xfbsh.fsf@vitty.brq.redhat.com>
On 30/04/20 13:33, Vitaly Kuznetsov wrote:
>> I would expect that it needs to keep it in a global variable anyway, but
>> yes this is a good point. You can also keep the ACK MSR and store the
>> pending bit in the other MSR, kind of like you have separate ISR and EOI
>> registers in the LAPIC.
>>
> Honestly I was inspired by Hyper-V's HV_X64_MSR_EOM MSR as the protocol
> we're trying to come up with here is very similar to HV messaging)
Oh, that's true actually.
> I'm not exactly sure why we need the pending bit after we drop #PF. When
> we call kvm_check_async_pf_completion() from MSR_KVM_ASYNC_PF_ACK write
> it will (in case there are page ready events in the queue) check if the
> slot is empty, put one there and raise IRQ regardless of guest's current
> state. It may or may not get injected immediately but we don't care.> The second invocation of kvm_check_async_pf_completion() from vcpu_run()
> will just go away.
You're right, you can just use the value in the guest to see if the
guest is ready. This is also similar to how #VE handles re-entrancy,
however because this is an interrupt we have IF to delay the IRQ until
after the interrupt handler has finished.
By dropping the #PF page ready case, we can also drop the ugly case
where WRMSR injects a page ready page fault even if IF=0. That one is
safe on Linux, but Andy didn't like it.
Paolo
next prev parent reply other threads:[~2020-04-30 11:43 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
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 [this message]
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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