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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: x86@kernel.org, kvm@vger.kernel.org,
	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 3/6] KVM: x86: interrupt based APF page-ready event delivery
Date: Thu, 30 Apr 2020 15:49:33 +0200	[thread overview]
Message-ID: <877dxxf5hu.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20200430132805.GB40678@xz-x1>

Peter Xu <peterx@redhat.com> writes:

> On Thu, Apr 30, 2020 at 10:31:32AM +0200, Vitaly Kuznetsov wrote:
>> as we need to write to two MSRs to configure the new mechanism ordering
>> becomes important. If the guest writes to ASYNC_PF_EN first to establish
>> the shared memory stucture the interrupt in ASYNC_PF2 is not yet set
>> (and AFAIR '0' is a valid interrupt!) so if an async pf happens
>> immediately after that we'll be forced to inject INT0 in the guest and
>> it'll get confused and linkely miss the event.
>> 
>> We can probably mandate the reverse sequence: guest has to set up
>> interrupt in ASYNC_PF2 first and then write to ASYNC_PF_EN (with both
>> bit 0 and bit 3). In that case the additional 'enable' bit in ASYNC_PF2
>> seems redundant. This protocol doesn't look too complex for guests to
>> follow.
>
> Yep looks good.  We should also update the document too about the fact.
>

Of course. It will also mention the fact that #PF-based mechanism is
now depreceted and unless guest opts into interrupt based delivery
async_pf is not functional (except for APF_HALT).

-- 
Vitaly


  reply	other threads:[~2020-04-30 13:49 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 [this message]
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
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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