From: "Michael S. Tsirkin" <mst@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Christophe de Dinechin <dinechin@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Yan Zhao <yan.y.zhao@intel.com>,
Alex Williamson <alex.williamson@redhat.com>,
Jason Wang <jasowang@redhat.com>,
Kevin Kevin <kevin.tian@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Lei Cao <lei.cao@stratus.com>
Subject: Re: [PATCH v3 12/21] KVM: X86: Implement ring-based dirty memory tracking
Date: Mon, 20 Jan 2020 02:47:46 -0500 [thread overview]
Message-ID: <20200120024717-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20200120072915.GD380565@xz-x1>
On Mon, Jan 20, 2020 at 03:29:15PM +0800, Peter Xu wrote:
> On Sun, Jan 19, 2020 at 05:12:35AM -0500, Michael S. Tsirkin wrote:
> > On Sun, Jan 19, 2020 at 10:09:53AM +0100, Paolo Bonzini wrote:
> > > On 09/01/20 20:15, Peter Xu wrote:
> > > > Regarding dropping the indices: I feel like it can be done, though we
> > > > probably need two extra bits for each GFN entry, for example:
> > > >
> > > > - Bit 0 of the GFN address to show whether this is a valid publish
> > > > of dirty gfn
> > > >
> > > > - Bit 1 of the GFN address to show whether this is collected by the
> > > > user
> > >
> > > We can use bit 62 and 63 of the GFN.
> >
> > If we are short on bits we can just use 1 bit. E.g. set if
> > userspace has collected the GFN.
>
> I'm still unsure whether we can use only one bit for this. Say,
> otherwise how does the userspace knows the entry is valid? For
> example, the entry with all zeros ({.slot = 0, gfn = 0}) could be
> recognized as a valid dirty page on slot 0 gfn 0, even if it's
> actually an unused entry.
So I guess the reverse: valid entry has bit set, userspace sets it to
0 when it collects it?
> >
> > > I think this can be done in a secure way. Later in the thread you say:
> > >
> > > > We simply check fetch_index (sorry I
> > > > meant this when I said reset_index, anyway it's the only index that we
> > > > expose to userspace) to make sure:
> > > >
> > > > reset_index <= fetch_index <= dirty_index
> > >
> > > So this means that KVM_RESET_DIRTY_RINGS should only test the "collected
> > > by user" flag on dirty ring entries between reset_index and dirty_index.
> > >
> > > Also I would make it
> > >
> > > 00b (invalid GFN) ->
> > > 01b (valid gfn published by kernel, which is dirty) ->
> > > 1*b (gfn dirty page collected by userspace) ->
> > > 00b (gfn reset by kernel, so goes back to invalid gfn)
> > > That is 10b and 11b are equivalent. The kernel doesn't read that bit if
> > > userspace has collected the page.
>
> Yes "1*b" is good too (IMHO as long as we can define three states for
> an entry). However do you want me to change to that? Note that I
> still think we need to read the rest of the field (in this case,
> "slot" and "gfn") besides the two bits to do re-protect. Should we
> trust that unconditionally if writable?
>
> Thanks,
>
> --
> Peter Xu
next prev parent reply other threads:[~2020-01-20 7:48 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-09 14:57 [PATCH v3 00/21] KVM: Dirty ring interface Peter Xu
2020-01-09 14:57 ` [PATCH v3 01/21] vfio: introduce vfio_iova_rw to read/write a range of IOVAs Peter Xu
2020-01-09 14:57 ` [PATCH v3 02/21] drm/i915/gvt: subsitute kvm_read/write_guest with vfio_iova_rw Peter Xu
2020-01-09 14:57 ` [PATCH v3 03/21] KVM: Remove kvm_read_guest_atomic() Peter Xu
2020-01-09 14:57 ` [PATCH v3 04/21] KVM: Add build-time error check on kvm_run size Peter Xu
2020-01-09 14:57 ` [PATCH v3 05/21] KVM: X86: Change parameter for fast_page_fault tracepoint Peter Xu
2020-01-09 14:57 ` [PATCH v3 06/21] KVM: X86: Don't take srcu lock in init_rmode_identity_map() Peter Xu
2020-01-09 14:57 ` [PATCH v3 07/21] KVM: Cache as_id in kvm_memory_slot Peter Xu
2020-01-09 14:57 ` [PATCH v3 08/21] KVM: X86: Drop x86_set_memory_region() Peter Xu
2020-01-09 14:57 ` [PATCH v3 09/21] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR] Peter Xu
2020-01-19 9:01 ` Paolo Bonzini
2020-01-20 6:45 ` Peter Xu
2020-01-21 15:56 ` Sean Christopherson
2020-01-21 16:14 ` Paolo Bonzini
2020-01-28 5:50 ` Peter Xu
2020-01-28 18:24 ` Sean Christopherson
2020-01-31 15:08 ` Peter Xu
2020-01-31 19:33 ` Sean Christopherson
2020-01-31 20:28 ` Peter Xu
2020-01-31 20:36 ` Sean Christopherson
2020-01-31 20:55 ` Peter Xu
2020-01-31 21:29 ` Sean Christopherson
2020-01-31 22:16 ` Peter Xu
2020-01-31 22:20 ` Sean Christopherson
2020-01-09 14:57 ` [PATCH v3 10/21] KVM: Pass in kvm pointer into mark_page_dirty_in_slot() Peter Xu
2020-01-09 14:57 ` [PATCH v3 11/21] KVM: Move running VCPU from ARM to common code Peter Xu
2020-01-09 14:57 ` [PATCH v3 12/21] KVM: X86: Implement ring-based dirty memory tracking Peter Xu
2020-01-09 16:29 ` Michael S. Tsirkin
2020-01-09 16:56 ` Alex Williamson
2020-01-09 19:21 ` Peter Xu
2020-01-09 19:36 ` Michael S. Tsirkin
2020-01-09 19:15 ` Peter Xu
2020-01-09 19:35 ` Michael S. Tsirkin
2020-01-09 20:19 ` Peter Xu
2020-01-09 22:18 ` Michael S. Tsirkin
2020-01-10 15:29 ` Peter Xu
2020-01-12 6:24 ` Michael S. Tsirkin
2020-01-14 20:01 ` Peter Xu
2020-01-15 6:50 ` Michael S. Tsirkin
2020-01-15 15:20 ` Peter Xu
2020-01-19 9:09 ` Paolo Bonzini
2020-01-19 10:12 ` Michael S. Tsirkin
2020-01-20 7:29 ` Peter Xu
2020-01-20 7:47 ` Michael S. Tsirkin [this message]
2020-01-21 8:29 ` Peter Xu
2020-01-21 10:25 ` Paolo Bonzini
2020-01-21 10:24 ` Paolo Bonzini
2020-01-11 4:49 ` kbuild test robot
2020-01-11 23:19 ` kbuild test robot
2020-01-15 6:47 ` Michael S. Tsirkin
2020-01-15 15:27 ` Peter Xu
2020-01-16 8:38 ` Michael S. Tsirkin
2020-01-16 16:27 ` Peter Xu
2020-01-17 9:50 ` Michael S. Tsirkin
2020-01-20 6:48 ` Peter Xu
2020-01-09 14:57 ` [PATCH v3 13/21] KVM: Make dirty ring exclusive to dirty bitmap log Peter Xu
2020-01-09 14:57 ` [PATCH v3 14/21] KVM: Don't allocate dirty bitmap if dirty ring is enabled Peter Xu
2020-01-09 16:41 ` Peter Xu
2020-01-09 14:57 ` [PATCH v3 15/21] KVM: selftests: Always clear dirty bitmap after iteration Peter Xu
2020-01-09 14:57 ` [PATCH v3 16/21] KVM: selftests: Sync uapi/linux/kvm.h to tools/ Peter Xu
2020-01-09 14:57 ` [PATCH v3 17/21] KVM: selftests: Use a single binary for dirty/clear log test Peter Xu
2020-01-09 14:57 ` [PATCH v3 18/21] KVM: selftests: Introduce after_vcpu_run hook for dirty " Peter Xu
2020-01-09 14:57 ` [PATCH v3 19/21] KVM: selftests: Add dirty ring buffer test Peter Xu
2020-01-09 14:57 ` [PATCH v3 20/21] KVM: selftests: Let dirty_log_test async for dirty ring test Peter Xu
2020-01-09 14:57 ` [PATCH v3 21/21] KVM: selftests: Add "-c" parameter to dirty log test Peter Xu
2020-01-09 15:59 ` [PATCH v3 00/21] KVM: Dirty ring interface Michael S. Tsirkin
2020-01-09 16:17 ` Peter Xu
2020-01-09 16:40 ` Michael S. Tsirkin
2020-01-09 17:08 ` Peter Xu
2020-01-09 19:08 ` Michael S. Tsirkin
2020-01-09 19:39 ` Peter Xu
2020-01-09 20:42 ` Paolo Bonzini
2020-01-09 22:28 ` Michael S. Tsirkin
2020-01-10 15:10 ` Peter Xu
2020-01-09 16:47 ` Alex Williamson
2020-01-09 17:58 ` Peter Xu
2020-01-09 19:13 ` Michael S. Tsirkin
2020-01-09 19:23 ` Peter Xu
2020-01-09 19:37 ` Michael S. Tsirkin
2020-01-09 20:51 ` Paolo Bonzini
2020-01-09 22:21 ` Michael S. Tsirkin
2020-01-19 9:11 ` Paolo Bonzini
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