From: Cornelia Huck <cohuck@redhat.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Kirti Wankhede <kwankhede@nvidia.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>, <cjia@nvidia.com>,
<kevin.tian@intel.com>, <ziye.yang@intel.com>,
<changpeng.liu@intel.com>, <yi.l.liu@intel.com>,
<mlevitsk@redhat.com>, <eskultet@redhat.com>,
<jonathan.davies@nutanix.com>, <eauger@redhat.com>,
<aik@ozlabs.ru>, <pasic@linux.ibm.com>, <felipe@nutanix.com>,
<Zhengxiao.zx@alibaba-inc.com>, <shuangtai.tst@alibaba-inc.com>,
<Ken.Xue@amd.com>, <zhi.a.wang@intel.com>, <yan.y.zhao@intel.com>,
<qemu-devel@nongnu.org>, <kvm@vger.kernel.org>
Subject: Re: [PATCH v10 Kernel 1/5] vfio: KABI for migration interface for device state
Date: Wed, 8 Jan 2020 15:59:55 +0100 [thread overview]
Message-ID: <20200108155955.78e908c1.cohuck@redhat.com> (raw)
In-Reply-To: <20200107115602.25156c41@w520.home>
On Tue, 7 Jan 2020 11:56:02 -0700
Alex Williamson <alex.williamson@redhat.com> wrote:
> On Tue, 7 Jan 2020 23:23:17 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
> > There are 3 invalid states:
> > * 101b => Invalid state
> > * 110b => Invalid state
> > * 111b => Invalid state
> >
> > why only 110b should be used to report error from vendor driver to
> > report error? Aren't we adding more confusions in the interface?
>
> I think the only chance of confusion is poor documentation. If we
> define all of the above as invalid and then say any invalid state
> indicates an error condition, then the burden is on the user to
> enumerate all the invalid states. That's not a good idea. Instead we
> could say 101b (_RESUMING|_RUNNING) is reserved, it's not currently
> used but it might be useful some day. Therefore there are no valid
> transitions into or out of this state. A vendor driver should fail a
> write(2) attempting to enter this state.
>
> That leaves 11Xb, where we consider _RESUMING and _SAVING as mutually
> exclusive, so neither are likely to ever be valid states. Logically,
> if the device is in a failed state such that it needs to be reset to be
> recovered, I would hope the device is not running, so !_RUNNING (110b)
> seems appropriate. I'm not sure we need that level of detail yet
> though, so I was actually just assuming both 11Xb states would indicate
> an error state and the undefined _RUNNING bit might differentiate
> something in the future.
>
> Therefore, I think we'd have:
>
> * 101b => Reserved
> * 11Xb => Error
>
> Where the device can only self transition into the Error state on a
> failed device_state transition and the only exit from the Error state
> is via the reset ioctl. The Reserved state is unreachable. The vendor
> driver must error on device_state writes to enter or exit the Error
> state and must error on writes to enter Reserved states. Is that still
> confusing?
I think one thing we could do is start to tie the meaning more to the
actual state (bit combination) and less to the individual bits. I.e.
- bit 0 indicates 'running',
- bit 1 indicates 'saving',
- bit 2 indicates 'resuming',
- bits 3-31 are reserved. [Aside: reserved-and-ignored or
reserved-and-must-be-zero?]
[Note that I don't specify what happens when a bit is set or unset.]
States are then defined as:
000b => stopped state (not saving or resuming)
001b => running state (not saving or resuming)
010b => stop-and-copy state
011b => pre-copy state
100b => resuming state
[Transitions between these states defined, as before.]
101b => reserved [for post-copy; no transitions defined]
111b => reserved [state does not make sense; no transitions defined]
110b => error state [state does not make sense per se, but it does not
indicate running; transitions into this state *are* possible]
To a 'reserved' state, we can later assign a different meaning (we
could even re-use 111b for a different error state, if needed); while
the error state must always stay the error state.
We should probably use some kind of feature indication to signify
whether a 'reserved' state actually has a meaning. Also, maybe we also
should designate the states > 111b as 'reserved'.
Does that make sense?
next prev parent reply other threads:[~2020-01-08 15:00 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-16 20:21 [PATCH v10 Kernel 0/5] KABIs to support migration for VFIO devices Kirti Wankhede
2019-12-16 20:21 ` [PATCH v10 Kernel 1/5] vfio: KABI for migration interface for device state Kirti Wankhede
2019-12-16 22:44 ` Alex Williamson
2019-12-17 6:28 ` Kirti Wankhede
2019-12-17 7:12 ` Yan Zhao
2019-12-17 18:43 ` Alex Williamson
2019-12-19 16:08 ` Kirti Wankhede
2019-12-19 17:27 ` Alex Williamson
2019-12-19 20:10 ` Kirti Wankhede
2019-12-19 21:09 ` Alex Williamson
2020-01-02 18:25 ` Dr. David Alan Gilbert
2020-01-06 23:18 ` Alex Williamson
2020-01-07 7:28 ` Kirti Wankhede
2020-01-07 17:09 ` Alex Williamson
2020-01-07 17:53 ` Kirti Wankhede
2020-01-07 18:56 ` Alex Williamson
2020-01-08 14:59 ` Cornelia Huck [this message]
2020-01-08 18:31 ` Alex Williamson
2020-01-08 20:41 ` Kirti Wankhede
2020-01-08 22:44 ` Alex Williamson
2020-01-10 14:21 ` Cornelia Huck
2020-01-07 9:57 ` Dr. David Alan Gilbert
2020-01-07 16:54 ` Alex Williamson
2020-01-07 17:50 ` Dr. David Alan Gilbert
2019-12-16 20:21 ` [PATCH v10 Kernel 2/5] vfio iommu: Adds flag to indicate dirty pages tracking capability support Kirti Wankhede
2019-12-16 23:16 ` Alex Williamson
2019-12-17 6:32 ` Kirti Wankhede
2019-12-16 20:21 ` [PATCH v10 Kernel 3/5] vfio iommu: Add ioctl defination for dirty pages tracking Kirti Wankhede
2019-12-16 20:21 ` [PATCH v10 Kernel 4/5] vfio iommu: Implementation of ioctl to " Kirti Wankhede
2019-12-17 5:15 ` Yan Zhao
2019-12-17 9:24 ` Kirti Wankhede
2019-12-17 9:51 ` Yan Zhao
2019-12-17 11:47 ` Kirti Wankhede
2019-12-18 1:04 ` Yan Zhao
2019-12-18 20:05 ` Dr. David Alan Gilbert
2019-12-19 0:57 ` Yan Zhao
2019-12-19 16:21 ` Kirti Wankhede
2019-12-20 0:58 ` Yan Zhao
2020-01-03 19:44 ` Dr. David Alan Gilbert
2020-01-04 3:53 ` Yan Zhao
2019-12-18 21:39 ` Alex Williamson
2019-12-19 18:42 ` Kirti Wankhede
2019-12-19 18:56 ` Alex Williamson
2019-12-16 20:21 ` [PATCH v10 Kernel 5/5] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap Kirti Wankhede
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