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From: Peter Xu <peterx@redhat.com>
To: Christophe de Dinechin <christophe.de.dinechin@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking
Date: Fri, 20 Dec 2019 13:19:14 -0500
Message-ID: <20191220181914.GB3780@xz-x1> (raw)
In-Reply-To: <20191213202324.GI16429@xz-x1>

On Fri, Dec 13, 2019 at 03:23:24PM -0500, Peter Xu wrote:
> > > +If one of the ring buffers is full, the guest will exit to userspace
> > > +with the exit reason set to KVM_EXIT_DIRTY_LOG_FULL, and the
> > > +KVM_RUN ioctl will return -EINTR. Once that happens, userspace
> > > +should pause all the vcpus, then harvest all the dirty pages and
> > > +rearm the dirty traps. It can unpause the guest after that.
> > 
> > Except for the condition above, why is it necessary to pause other VCPUs
> > than the one being harvested?
> 
> This is a good question.  Paolo could correct me if I'm wrong.
> 
> Firstly I think this should rarely happen if the userspace is
> collecting the dirty bits from time to time.  If it happens, we'll
> need to call KVM_RESET_DIRTY_RINGS to reset all the rings.  Then the
> question actually becomes to: Whether we'd like to have per-vcpu
> KVM_RESET_DIRTY_RINGS?

Hmm when I'm rethinking this, I could have errornously deduced
something from Christophe's question.  Christophe was asking about why
kicking other vcpus, while it does not mean that the RESET will need
to do per-vcpu.

So now I tend to agree here with Christophe that I can't find a reason
why we need to kick all vcpus out.  Even if we need to do tlb flushing
for all vcpus when RESET, we can simply collect all the rings before
sending the RESET, then it's not really a reason to explicitly kick
them from userspace.  So I plan to remove this sentence in the next
version (which is only a document update).

-- 
Peter Xu


  parent reply index

Thread overview: 121+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-29 21:34 [PATCH RFC 00/15] KVM: Dirty ring interface Peter Xu
2019-11-29 21:34 ` [PATCH RFC 01/15] KVM: Move running VCPU from ARM to common code Peter Xu
2019-12-03 19:01   ` Sean Christopherson
2019-12-04  9:42     ` Paolo Bonzini
2019-12-09 22:05       ` Peter Xu
2019-11-29 21:34 ` [PATCH RFC 02/15] KVM: Add kvm/vcpu argument to mark_dirty_page_in_slot Peter Xu
2019-12-02 19:32   ` Sean Christopherson
2019-12-02 20:49     ` Peter Xu
2019-11-29 21:34 ` [PATCH RFC 03/15] KVM: Add build-time error check on kvm_run size Peter Xu
2019-12-02 19:30   ` Sean Christopherson
2019-12-02 20:53     ` Peter Xu
2019-12-02 22:19       ` Sean Christopherson
2019-12-02 22:40         ` Peter Xu
2019-12-03  5:50           ` Sean Christopherson
2019-12-03 13:41         ` Paolo Bonzini
2019-12-03 17:04           ` Peter Xu
2019-11-29 21:34 ` [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking Peter Xu
2019-12-02 20:10   ` Sean Christopherson
2019-12-02 21:16     ` Peter Xu
2019-12-02 21:50       ` Sean Christopherson
2019-12-02 23:09         ` Peter Xu
2019-12-03 13:48         ` Paolo Bonzini
2019-12-03 18:46           ` Sean Christopherson
2019-12-04 10:05             ` Paolo Bonzini
2019-12-07  0:29               ` Sean Christopherson
2019-12-09  9:37                 ` Paolo Bonzini
2019-12-09 21:54               ` Peter Xu
2019-12-10 10:07                 ` Paolo Bonzini
2019-12-10 15:52                   ` Peter Xu
2019-12-10 17:09                     ` Paolo Bonzini
2019-12-15 17:21                       ` Peter Xu
2019-12-16 10:08                         ` Paolo Bonzini
2019-12-16 18:54                           ` Peter Xu
2019-12-17  9:01                             ` Paolo Bonzini
2019-12-17 16:24                               ` Peter Xu
2019-12-17 16:28                                 ` Paolo Bonzini
2019-12-18 21:58                                   ` Peter Xu
2019-12-18 22:24                                     ` Sean Christopherson
2019-12-18 22:37                                       ` Paolo Bonzini
2019-12-18 22:49                                         ` Peter Xu
2019-12-17  2:28                           ` Tian, Kevin
2019-12-17 16:18                             ` Alex Williamson
2019-12-17 16:30                               ` Paolo Bonzini
2019-12-18  0:29                                 ` Tian, Kevin
     [not found]                           ` <AADFC41AFE54684AB9EE6CBC0274A5D19D645E5F@SHSMSX104.ccr.corp.intel.com>
2019-12-17  5:17                             ` Tian, Kevin
2019-12-17  5:25                               ` Yan Zhao
2019-12-17 16:24                                 ` Alex Williamson
2019-12-03 19:13   ` Sean Christopherson
2019-12-04 10:14     ` Paolo Bonzini
2019-12-04 14:33       ` Sean Christopherson
2019-12-04 10:38   ` Jason Wang
2019-12-04 11:04     ` Paolo Bonzini
2019-12-04 19:52       ` Peter Xu
2019-12-05  6:51         ` Jason Wang
2019-12-05 12:08           ` Peter Xu
2019-12-05 13:12             ` Jason Wang
2019-12-10 13:25       ` Michael S. Tsirkin
2019-12-10 13:31         ` Paolo Bonzini
2019-12-10 16:02           ` Peter Xu
2019-12-10 21:53             ` Michael S. Tsirkin
2019-12-11  9:05               ` Paolo Bonzini
2019-12-11 13:04                 ` Michael S. Tsirkin
2019-12-11 14:54                   ` Peter Xu
2019-12-10 21:48           ` Michael S. Tsirkin
2019-12-11 12:53   ` Michael S. Tsirkin
2019-12-11 14:14     ` Paolo Bonzini
2019-12-11 20:59     ` Peter Xu
2019-12-11 22:57       ` Michael S. Tsirkin
2019-12-12  0:08         ` Paolo Bonzini
2019-12-12  7:36           ` Michael S. Tsirkin
2019-12-12  8:12             ` Paolo Bonzini
2019-12-12 10:38               ` Michael S. Tsirkin
2019-12-15 17:33           ` Peter Xu
2019-12-16  9:47             ` Michael S. Tsirkin
2019-12-16 15:07               ` Peter Xu
2019-12-16 15:33                 ` Michael S. Tsirkin
2019-12-16 15:47                   ` Peter Xu
2019-12-11 17:24   ` Christophe de Dinechin
2019-12-13 20:23     ` Peter Xu
2019-12-14  7:57       ` Paolo Bonzini
2019-12-14 16:26         ` Peter Xu
2019-12-16  9:29           ` Paolo Bonzini
2019-12-16 15:26             ` Peter Xu
2019-12-16 15:31               ` Paolo Bonzini
2019-12-16 15:43                 ` Peter Xu
2019-12-17 12:16         ` Christophe de Dinechin
2019-12-17 12:19           ` Paolo Bonzini
2019-12-17 15:38             ` Peter Xu
2019-12-17 16:31               ` Paolo Bonzini
2019-12-17 16:42                 ` Peter Xu
2019-12-17 16:48                   ` Paolo Bonzini
2019-12-17 19:41                     ` Peter Xu
2019-12-18  0:33                       ` Paolo Bonzini
2019-12-18 16:32                         ` Peter Xu
2019-12-18 16:41                           ` Paolo Bonzini
2019-12-20 18:19       ` Peter Xu [this message]
2019-11-29 21:34 ` [PATCH RFC 05/15] KVM: Make dirty ring exclusive to dirty bitmap log Peter Xu
2019-11-29 21:34 ` [PATCH RFC 06/15] KVM: Introduce dirty ring wait queue Peter Xu
2019-11-29 21:34 ` [PATCH RFC 07/15] KVM: X86: Implement ring-based dirty memory tracking Peter Xu
2019-11-29 21:34 ` [PATCH RFC 08/15] KVM: selftests: Always clear dirty bitmap after iteration Peter Xu
2019-11-29 21:34 ` [PATCH RFC 09/15] KVM: selftests: Sync uapi/linux/kvm.h to tools/ Peter Xu
2019-11-29 21:35 ` [PATCH RFC 10/15] KVM: selftests: Use a single binary for dirty/clear log test Peter Xu
2019-11-29 21:35 ` [PATCH RFC 11/15] KVM: selftests: Introduce after_vcpu_run hook for dirty " Peter Xu
2019-11-29 21:35 ` [PATCH RFC 12/15] KVM: selftests: Add dirty ring buffer test Peter Xu
2019-11-29 21:35 ` [PATCH RFC 13/15] KVM: selftests: Let dirty_log_test async for dirty ring test Peter Xu
2019-11-29 21:35 ` [PATCH RFC 14/15] KVM: selftests: Add "-c" parameter to dirty log test Peter Xu
2019-11-29 21:35 ` [PATCH RFC 15/15] KVM: selftests: Test dirty ring waitqueue Peter Xu
2019-11-30  8:29 ` [PATCH RFC 00/15] KVM: Dirty ring interface Paolo Bonzini
2019-12-02  2:13   ` Peter Xu
2019-12-03 13:59     ` Paolo Bonzini
2019-12-05 19:30       ` Peter Xu
2019-12-05 19:59         ` Paolo Bonzini
2019-12-05 20:52           ` Peter Xu
2019-12-02 20:21   ` Sean Christopherson
2019-12-02 20:43     ` Peter Xu
2019-12-04 10:39 ` Jason Wang
2019-12-04 19:33   ` Peter Xu
2019-12-05  6:49     ` Jason Wang
2019-12-11 13:41 ` Christophe de Dinechin
2019-12-11 14:16   ` Paolo Bonzini
2019-12-11 17:15     ` Peter Xu

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