From: Vivek Goyal <vgoyal@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, x86@kernel.org,
Paolo Bonzini <pbonzini@redhat.com>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
Wanpeng Li <wanpengli@tencent.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Jim Mattson <jmattson@google.com>, Gavin Shan <gshan@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/8] KVM: x86: interrupt based APF page-ready event delivery
Date: Thu, 14 May 2020 09:31:57 -0400 [thread overview]
Message-ID: <20200514133157.GB206709@redhat.com> (raw)
In-Reply-To: <87zhabdjlm.fsf@vitty.brq.redhat.com>
On Thu, May 14, 2020 at 10:08:37AM +0200, Vitaly Kuznetsov wrote:
> Vivek Goyal <vgoyal@redhat.com> writes:
>
> > On Wed, May 13, 2020 at 04:23:55PM +0200, Vitaly Kuznetsov wrote:
> >
> > [..]
> >> >> Also,
> >> >> kdump kernel may not even support APF so it will get very confused when
> >> >> APF events get delivered.
> >> >
> >> > New kernel can just ignore these events if it does not support async
> >> > pf?
> >> >
> >> > This is somewhat similar to devices still doing interrupts in new
> >> > kernel. And solution for that seemed to be doing a "reset" of devices
> >> > in new kernel. We probably need similar logic where in new kernel
> >> > we simply disable "async pf" so that we don't get new notifications.
> >>
> >> Right and that's what we're doing - just disabling new notifications.
> >
> > Nice.
> >
> > So why there is a need to deliver "page ready" notifications
> > to guest after guest has disabled async pf. Atleast kdump does not
> > seem to need it. It will boot into second kernel anyway, irrespective
> > of the fact whether it receives page ready or not.
>
> We don't deliver anything to the guest after it disables APF (neither
> 'page ready' for what was previously missing, nor 'page not ready' for
> new faults), kvm_arch_can_inject_async_page_present() is just another
> misnomer, it should be named something like
> 'kvm_arch_can_unqueue_async_page_present()' meaning that 'page ready'
> notification can be 'unqueued' from internal KVM queue. We will either
> deliver it (when guest has APF enabled) or just drop it (when guest has
> APF disabled). The only case when it has to stay in the queue is when
> guest has APF enabled and the slot is still busy (so it didn't get to
> process a previously delivered notification). We will try to deliver it
> again after guest writes to MSR_KVM_ASYNC_PF_ACK.
This makes sense. Renaming this function to make it more clear will
help understanding code better.
Vivek
next prev parent reply other threads:[~2020-05-14 13:32 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-11 16:47 [PATCH 0/8] KVM: x86: Interrupt-based mechanism for async_pf 'page present' notifications Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 1/8] Revert "KVM: async_pf: Fix #DF due to inject "Page not Present" and "Page Ready" exceptions simultaneously" Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 2/8] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info Vitaly Kuznetsov
2020-05-12 15:27 ` Vivek Goyal
2020-05-12 15:40 ` Vitaly Kuznetsov
2020-05-12 15:53 ` Vivek Goyal
2020-05-12 17:50 ` Sean Christopherson
2020-05-13 9:09 ` Vitaly Kuznetsov
2020-05-13 12:52 ` Vivek Goyal
2020-05-15 15:59 ` Paolo Bonzini
2020-05-15 18:46 ` Sean Christopherson
2020-05-15 19:18 ` Paolo Bonzini
2020-05-15 20:33 ` Vivek Goyal
2020-05-15 20:53 ` Sean Christopherson
2020-05-15 20:43 ` Sean Christopherson
2020-05-15 22:23 ` Paolo Bonzini
2020-05-15 23:16 ` Sean Christopherson
2020-05-21 14:59 ` Vitaly Kuznetsov
2020-05-22 7:33 ` Paolo Bonzini
2020-05-12 21:15 ` Vivek Goyal
2020-05-21 18:38 ` Vivek Goyal
2020-05-23 16:34 ` Vitaly Kuznetsov
2020-05-26 12:50 ` Vivek Goyal
2020-05-11 16:47 ` [PATCH 3/8] KVM: introduce kvm_read_guest_offset_cached() Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 4/8] KVM: x86: interrupt based APF page-ready event delivery Vitaly Kuznetsov
2020-05-12 14:24 ` Vivek Goyal
2020-05-12 15:50 ` Vitaly Kuznetsov
2020-05-12 18:07 ` Vivek Goyal
2020-05-13 9:03 ` Vitaly Kuznetsov
2020-05-13 13:53 ` Vivek Goyal
2020-05-13 14:03 ` Vivek Goyal
2020-05-13 14:23 ` Vitaly Kuznetsov
2020-05-13 18:46 ` Vivek Goyal
2020-05-14 8:08 ` Vitaly Kuznetsov
2020-05-14 13:31 ` Vivek Goyal [this message]
2020-05-11 16:47 ` [PATCH 5/8] KVM: x86: acknowledgment mechanism for async pf page ready notifications Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 6/8] KVM: x86: announce KVM_FEATURE_ASYNC_PF_INT Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 7/8] KVM: x86: Switch KVM guest to using interrupts for page ready APF delivery Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 8/8] KVM: x86: drop KVM_PV_REASON_PAGE_READY case from kvm_handle_page_fault() Vitaly Kuznetsov
2020-05-12 15:32 ` [PATCH 0/8] KVM: x86: Interrupt-based mechanism for async_pf 'page present' notifications Vivek Goyal
2020-05-12 16:12 ` Vitaly Kuznetsov
2020-05-13 14:16 ` Vivek Goyal
2020-05-14 18:14 ` Vitaly Kuznetsov
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