From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
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>,
Jim Mattson <jmattson@google.com>, Gavin Shan <gshan@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/8] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info
Date: Tue, 12 May 2020 10:50:17 -0700 [thread overview]
Message-ID: <20200512175017.GC12100@linux.intel.com> (raw)
In-Reply-To: <20200512155339.GD138129@redhat.com>
On Tue, May 12, 2020 at 11:53:39AM -0400, Vivek Goyal wrote:
> On Tue, May 12, 2020 at 05:40:10PM +0200, Vitaly Kuznetsov wrote:
> > Vivek Goyal <vgoyal@redhat.com> writes:
> >
> > > On Mon, May 11, 2020 at 06:47:46PM +0200, Vitaly Kuznetsov wrote:
> > >> Currently, APF mechanism relies on the #PF abuse where the token is being
> > >> passed through CR2. If we switch to using interrupts to deliver page-ready
> > >> notifications we need a different way to pass the data. Extent the existing
> > >> 'struct kvm_vcpu_pv_apf_data' with token information for page-ready
> > >> notifications.
> > >>
> > >> The newly introduced apf_put_user_ready() temporary puts both reason
> > >> and token information, this will be changed to put token only when we
> > >> switch to interrupt based notifications.
> > >>
> > >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> > >> ---
> > >> arch/x86/include/uapi/asm/kvm_para.h | 3 ++-
> > >> arch/x86/kvm/x86.c | 17 +++++++++++++----
> > >> 2 files changed, 15 insertions(+), 5 deletions(-)
> > >>
> > >> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> > >> index 2a8e0b6b9805..e3602a1de136 100644
> > >> --- a/arch/x86/include/uapi/asm/kvm_para.h
> > >> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> > >> @@ -113,7 +113,8 @@ struct kvm_mmu_op_release_pt {
> > >>
> > >> struct kvm_vcpu_pv_apf_data {
> > >> __u32 reason;
> > >> - __u8 pad[60];
> > >> + __u32 pageready_token;
> > >
> > > How about naming this just "token". That will allow me to deliver error
> > > as well. pageready_token name seems to imply that this will always be
> > > successful with page being ready.
> > >
> > > And reason will tell whether page could successfully be ready or
> > > it was an error. And token will help us identify the task which
> > > is waiting for the event.
> >
> > I added 'pageready_' prefix to make it clear this is not used for 'page
> > not present' notifications where we pass token through CR2. (BTW
> > 'reason' also becomes a misnomer because we can only see
> > 'KVM_PV_REASON_PAGE_NOT_PRESENT' there.)
>
> Sure. I am just trying to keep names in such a way so that we could
> deliver more events and not keep it too tightly coupled with only
> two events (page not present, page ready).
>
> >
> > I have no strong opinion, can definitely rename this to 'token' and add
> > a line to the documentation to re-state that this is not used for type 1
> > events.
>
> I don't even know why are we calling "type 1" and "type 2" event. Calling
> it KVM_PV_REASON_PAGE_NOT_PRESENT and KVM_PV_REASON_PAGE_READY event
> is much more intuitive. If somebody is confused about how event will
> be delivered, that could be part of documentation. And "type1" and "type2"
> does not say anything about delivery method anyway.
>
> Also, type of event should not necessarily be tied to delivery method.
> For example if we end up introducing say, "KVM_PV_REASON_PAGE_ERROR", then
> I would think that event can be injected both using exception (#PF or #VE)
> as well as interrupt (depending on state of system).
Why bother preserving backwards compatibility? AIUI, both KVM and guest
will support async #PF iff interrupt delivery is enabled. Why not make
the interrupt delivery approach KVM_ASYNC_PF_V2 and completely redefine the
ABI? E.g. to make it compatible with reflecting !PRESENT faults without a
VM-Exit via Intel's EPT Violation #VE?
next prev parent reply other threads:[~2020-05-12 17:50 UTC|newest]
Thread overview: 44+ 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 [this message]
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
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
2020-05-13 1:44 ` [kbuild-all] " kbuild test robot
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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