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From: Andy Lutomirski <luto@kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Vitaly Kuznetsov <vkuznets@redhat.com>, X86 ML <x86@kernel.org>,
	kvm list <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.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 17:45:16 -0700	[thread overview]
Message-ID: <CALCETrWQBmmVODuSXac965o29Oxqo6uo4Ujm2AN2FUMztwCnzA@mail.gmail.com> (raw)
In-Reply-To: <0de4a809-e965-d0ad-489f-5b011aa5bf89@redhat.com>

On Wed, Apr 29, 2020 at 10:40 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 29/04/20 19:28, Andy Lutomirski wrote:
> > 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.
>
> No, it would be much more complicated code for a slow path which is
> already order of magnitudes slower than a vmexit.  It would also use
> much more memory.

Fair enough.

>
> > It might be even better if a single unified data structure was used
> > for both notifications.
>
> That's a very bad idea since one is synchronous and one is asynchronous.
>  Part of the proposal we agreed upon was to keep "page not ready"
> synchronous while making "page ready" an interrupt.  The data structure
> for "page not ready" will be #VE.
>

#VE on SVM will be interesting, to say the least, and I think that a
solution that is VMX specific doesn't make much sense.  #VE also has
unpleasant issues involving the contexts in which it can occur.  You
will have quite a hard time convincing me to ack the addition of a #VE
entry handler for this.  I think a brand new vector is the right
solution.

  reply	other threads:[~2020-04-30  0:45 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 [this message]
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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