From: "Michael S. Tsirkin" <mst@redhat.com>
To: Paul Brook <paul@codesourcery.com>
Cc: qemu-devel@nongnu.org, Carsten Otte <cotte@de.ibm.com>,
kvm@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>,
virtualization@lists.linux-foundation.org,
Blue Swirl <blauwirbel@gmail.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Avi Kivity <avi@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions
Date: Wed, 10 Jun 2009 19:26:44 +0300 [thread overview]
Message-ID: <20090610162644.GJ28601@redhat.com> (raw)
In-Reply-To: <200906101708.27815.paul@codesourcery.com>
On Wed, Jun 10, 2009 at 05:08:15PM +0100, Paul Brook wrote:
> On Wednesday 10 June 2009, Michael S. Tsirkin wrote:
> > On Wed, Jun 10, 2009 at 04:15:04PM +0100, Paul Brook wrote:
> > > > > That's seems just plain wrong to me.
> > > > > Loading a VM shouldn't not
> > > > > do anything that can't happen during normal operation.
> > > >
> > > > At least wrt pci, we are very far from this state: load just overwrites
> > > > all registers, readonly or not, which can never happen during normal
> > > > operation.
> > >
> > > IMO that code is wrong. We should only be loading things that the guest
> > > can change (directly or indirectly).
> >
> > Making it work this way will mean that minor changes to a device can
> > break backwards compatibility with old images, often in surprising ways.
> > What are the advantages?
>
> If you can't create an identical machine from scratch then I don't consider
> snapshot/migration to be a useful feature. i.e. as soon as you shutdown and
> restart the guest it is liable to break anyway.
Why is liable to break?
Configuration does not change until you load another image.
Look here:
void msix_reset(PCIDevice *dev)
{
if (!(dev->cap_present & QEMU_PCI_CAP_MSIX))
return;
...
}
So once you load and image with MSIX capability off,
it will stay off across guest restarts.
> It may be that the snapshot/migration code wants to include a machine config,
> and create a new machine from that. However this is a separate issue, and
> arguably something your VM manager should be handling for you.
>
> Paul
Since the image already has a necessary information, duplicating
it in a separate machine config will just lead to errors.
--
MST
WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Paul Brook <paul@codesourcery.com>
Cc: Carsten Otte <cotte@de.ibm.com>,
kvm@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>,
qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org,
Blue Swirl <blauwirbel@gmail.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Avi Kivity <avi@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions
Date: Wed, 10 Jun 2009 19:26:44 +0300 [thread overview]
Message-ID: <20090610162644.GJ28601@redhat.com> (raw)
In-Reply-To: <200906101708.27815.paul@codesourcery.com>
On Wed, Jun 10, 2009 at 05:08:15PM +0100, Paul Brook wrote:
> On Wednesday 10 June 2009, Michael S. Tsirkin wrote:
> > On Wed, Jun 10, 2009 at 04:15:04PM +0100, Paul Brook wrote:
> > > > > That's seems just plain wrong to me.
> > > > > Loading a VM shouldn't not
> > > > > do anything that can't happen during normal operation.
> > > >
> > > > At least wrt pci, we are very far from this state: load just overwrites
> > > > all registers, readonly or not, which can never happen during normal
> > > > operation.
> > >
> > > IMO that code is wrong. We should only be loading things that the guest
> > > can change (directly or indirectly).
> >
> > Making it work this way will mean that minor changes to a device can
> > break backwards compatibility with old images, often in surprising ways.
> > What are the advantages?
>
> If you can't create an identical machine from scratch then I don't consider
> snapshot/migration to be a useful feature. i.e. as soon as you shutdown and
> restart the guest it is liable to break anyway.
Why is liable to break?
Configuration does not change until you load another image.
Look here:
void msix_reset(PCIDevice *dev)
{
if (!(dev->cap_present & QEMU_PCI_CAP_MSIX))
return;
...
}
So once you load and image with MSIX capability off,
it will stay off across guest restarts.
> It may be that the snapshot/migration code wants to include a machine config,
> and create a new machine from that. However this is a separate issue, and
> arguably something your VM manager should be handling for you.
>
> Paul
Since the image already has a necessary information, duplicating
it in a separate machine config will just lead to errors.
--
MST
next prev parent reply other threads:[~2009-06-10 16:30 UTC|newest]
Thread overview: 105+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1243253205.git.mst@redhat.com>
2009-05-25 12:12 ` [PATCHv2] qemu: make default_write_config use mask table Michael S. Tsirkin
2009-05-25 12:12 ` Michael S. Tsirkin
2009-05-25 12:12 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-25 12:24 ` [PATCH 01/11] " Michael S. Tsirkin
2009-05-25 12:24 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-25 12:24 ` Michael S. Tsirkin
2009-05-25 12:25 ` [PATCH 02/11] qemu: capability bits in pci save/restore Michael S. Tsirkin
2009-05-25 12:25 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-25 12:25 ` Michael S. Tsirkin
2009-05-25 12:25 ` [PATCH 03/11] qemu: add routines to manage PCI capabilities Michael S. Tsirkin
2009-05-25 12:25 ` Michael S. Tsirkin
2009-05-25 12:25 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-26 8:49 ` Isaku Yamahata
2009-05-26 8:49 ` Isaku Yamahata
2009-05-26 9:22 ` Michael S. Tsirkin
2009-05-26 9:22 ` Michael S. Tsirkin
2009-05-26 9:22 ` Michael S. Tsirkin
2009-05-26 8:49 ` Isaku Yamahata
2009-05-26 9:30 ` [PATCH] qemu: fix pci_find_capability for multiple caps Michael S. Tsirkin
2009-05-26 9:30 ` Michael S. Tsirkin
2009-05-26 9:30 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-25 12:25 ` [PATCH 04/11] qemu: helper routines for pci access Michael S. Tsirkin
2009-05-25 12:25 ` Michael S. Tsirkin
2009-05-25 12:25 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-26 2:33 ` Isaku Yamahata
2009-05-26 2:33 ` Isaku Yamahata
2009-05-26 6:41 ` Michael S. Tsirkin
2009-05-26 6:41 ` Michael S. Tsirkin
2009-05-26 8:07 ` Avi Kivity
2009-05-26 8:07 ` Avi Kivity
2009-05-26 8:49 ` Michael S. Tsirkin
2009-05-26 8:49 ` Michael S. Tsirkin
2009-05-26 8:49 ` Michael S. Tsirkin
2009-05-26 8:07 ` Avi Kivity
2009-05-26 6:41 ` Michael S. Tsirkin
2009-05-26 2:33 ` Isaku Yamahata
2009-05-25 12:25 ` [PATCH 05/11] qemu: MSI-X support functions Michael S. Tsirkin
2009-05-25 12:25 ` [Qemu-devel] " Michael S. Tsirkin
2009-06-09 23:19 ` Paul Brook
2009-06-09 23:19 ` Paul Brook
2009-06-10 9:46 ` Michael S. Tsirkin
2009-06-10 9:46 ` Michael S. Tsirkin
2009-06-10 9:46 ` Michael S. Tsirkin
2009-06-10 14:07 ` Paul Brook
2009-06-10 14:07 ` Paul Brook
2009-06-10 14:25 ` Michael S. Tsirkin
2009-06-10 14:25 ` Michael S. Tsirkin
2009-06-10 14:25 ` Michael S. Tsirkin
2009-06-10 14:39 ` Paul Brook
2009-06-10 14:39 ` Paul Brook
2009-06-10 14:47 ` Michael S. Tsirkin
2009-06-10 14:47 ` Michael S. Tsirkin
2009-06-10 14:47 ` Michael S. Tsirkin
2009-06-10 15:15 ` Paul Brook
2009-06-10 15:15 ` Paul Brook
2009-06-10 15:52 ` Michael S. Tsirkin
2009-06-10 15:52 ` Michael S. Tsirkin
2009-06-10 15:52 ` Michael S. Tsirkin
2009-06-10 16:08 ` Paul Brook
2009-06-10 16:08 ` Paul Brook
2009-06-10 16:26 ` Michael S. Tsirkin [this message]
2009-06-10 16:26 ` Michael S. Tsirkin
2009-06-10 16:46 ` Paul Brook
2009-06-10 16:46 ` Paul Brook
2009-06-10 17:03 ` Michael S. Tsirkin
2009-06-10 17:03 ` Michael S. Tsirkin
2009-06-10 17:30 ` Paul Brook
2009-06-10 17:30 ` Paul Brook
2009-06-10 17:30 ` Paul Brook
2009-06-10 18:07 ` Michael S. Tsirkin
2009-06-10 18:07 ` Michael S. Tsirkin
2009-06-10 18:07 ` Michael S. Tsirkin
2009-06-10 19:04 ` Paul Brook
2009-06-10 19:04 ` Paul Brook
2009-06-11 8:29 ` Michael S. Tsirkin
2009-06-11 8:29 ` Michael S. Tsirkin
2009-06-11 8:29 ` Michael S. Tsirkin
2009-06-10 19:04 ` Paul Brook
2009-06-10 17:03 ` Michael S. Tsirkin
2009-06-10 16:46 ` Paul Brook
2009-06-10 16:26 ` Michael S. Tsirkin
2009-06-10 16:08 ` Paul Brook
2009-06-10 15:15 ` Paul Brook
2009-06-10 14:39 ` Paul Brook
2009-06-10 14:07 ` Paul Brook
2009-06-09 23:19 ` Paul Brook
2009-05-25 12:25 ` Michael S. Tsirkin
2009-05-25 12:25 ` [PATCH 06/11] qemu: add flag to disable MSI-X by default Michael S. Tsirkin
2009-05-25 12:25 ` Michael S. Tsirkin
2009-05-25 12:25 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-25 12:25 ` [PATCH 07/11] qemu: minimal MSI/MSI-X implementation for PC Michael S. Tsirkin
2009-05-25 12:25 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-25 12:25 ` Michael S. Tsirkin
2009-05-25 12:26 ` [PATCH 08/11] qemu: add support for resizing regions Michael S. Tsirkin
2009-05-25 12:26 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-25 12:26 ` Michael S. Tsirkin
2009-05-25 12:26 ` [PATCH 09/11] qemu: virtio support for many interrupt vectors Michael S. Tsirkin
2009-05-25 12:26 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-25 12:26 ` Michael S. Tsirkin
2009-05-25 12:26 ` [PATCH 10/11] qemu: MSI-X support in virtio PCI Michael S. Tsirkin
2009-05-25 12:26 ` [Qemu-devel] " Michael S. Tsirkin
2009-05-25 12:26 ` Michael S. Tsirkin
2009-05-25 12:26 ` [PATCH 11/11] qemu: request 3 vectors in virtio-net Michael S. Tsirkin
2009-05-25 12:26 ` Michael S. Tsirkin
2009-05-25 12:26 ` [Qemu-devel] " Michael S. Tsirkin
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