| Message ID | 1456771254-17511-38-git-send-email-armbru@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Feb 29, 2016 at 7:40 PM, Markus Armbruster <armbru@redhat.com> wrote: > Migration with ivshmem needs to be carefully orchestrated to work. > Exactly one peer (the "master") migrates to the destination, all other > peers need to unplug (and disconnect), migrate, plug back (and > reconnect). This is sort of documented in qemu-doc. > > If peers connect on the destination before migration completes, the > shared memory can get messed up. This isn't documented anywhere. Fix > that in qemu-doc. > > To avoid messing up register IVPosition on migration, the server must > assign the same ID on source and destination. ivshmem-spec.txt leaves > ID assignment unspecified, however. > > Amend ivshmem-spec.txt to require the first client to receive ID zero. > The example ivshmem-server complies: it always assigns the first > unused ID. > > For a bit of additional safety, enforce ID zero for the master. This > does nothing when we're not using a server, because the ID is zero for > all peers then. > > Signed-off-by: Markus Armbruster <armbru@redhat.com> > --- Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> > docs/specs/ivshmem-spec.txt | 2 ++ > hw/misc/ivshmem.c | 6 ++++++ > qemu-doc.texi | 5 +++++ > 3 files changed, 13 insertions(+) > > diff --git a/docs/specs/ivshmem-spec.txt b/docs/specs/ivshmem-spec.txt > index 047dfc0..b062acd 100644 > --- a/docs/specs/ivshmem-spec.txt > +++ b/docs/specs/ivshmem-spec.txt > @@ -164,6 +164,8 @@ For each new client that connects to the server, the server > - sends interrupt setup messages to the new client (these contain file > descriptors for receiving interrupts). > > +The first client to connect to the server receives ID zero. > + > When a client disconnects from the server, the server sends disconnect > notifications to the other clients. > > diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c > index f6fce15..9a292e5 100644 > --- a/hw/misc/ivshmem.c > +++ b/hw/misc/ivshmem.c > @@ -869,6 +869,12 @@ static void ivshmem_common_realize(PCIDevice *dev, Error **errp) > return; > } > > + if (s->master == ON_OFF_AUTO_ON && s->vm_id != 0) { > + error_setg(errp, > + "master must connect to the server before any peers"); > + return; > + } > + > qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive, > ivshmem_read, NULL, s); > > diff --git a/qemu-doc.texi b/qemu-doc.texi > index 0dd01c7..79141d3 100644 > --- a/qemu-doc.texi > +++ b/qemu-doc.texi > @@ -1295,12 +1295,17 @@ When using the server, the guest will be assigned a VM ID (>=0) that allows gues > using the same server to communicate via interrupts. Guests can read their > VM ID from a device register (see ivshmem-spec.txt). > > +@subsubsection Migration with ivshmem > + > With device property @option{master=on}, the guest will copy the shared > memory on migration to the destination host. With @option{master=off}, > the guest will not be able to migrate with the device attached. In the > latter case, the device should be detached and then reattached after > migration using the PCI hotplug support. > > +At most one of the devices sharing the same memory can be master. The > +master must complete migration before you plug back the other devices. > + > @subsubsection ivshmem and hugepages > > Instead of specifying the <shm size> using POSIX shm, you may specify > -- > 2.4.3 > >
diff --git a/docs/specs/ivshmem-spec.txt b/docs/specs/ivshmem-spec.txt index 047dfc0..b062acd 100644 --- a/docs/specs/ivshmem-spec.txt +++ b/docs/specs/ivshmem-spec.txt @@ -164,6 +164,8 @@ For each new client that connects to the server, the server - sends interrupt setup messages to the new client (these contain file descriptors for receiving interrupts). +The first client to connect to the server receives ID zero. + When a client disconnects from the server, the server sends disconnect notifications to the other clients. diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c index f6fce15..9a292e5 100644 --- a/hw/misc/ivshmem.c +++ b/hw/misc/ivshmem.c @@ -869,6 +869,12 @@ static void ivshmem_common_realize(PCIDevice *dev, Error **errp) return; } + if (s->master == ON_OFF_AUTO_ON && s->vm_id != 0) { + error_setg(errp, + "master must connect to the server before any peers"); + return; + } + qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive, ivshmem_read, NULL, s); diff --git a/qemu-doc.texi b/qemu-doc.texi index 0dd01c7..79141d3 100644 --- a/qemu-doc.texi +++ b/qemu-doc.texi @@ -1295,12 +1295,17 @@ When using the server, the guest will be assigned a VM ID (>=0) that allows gues using the same server to communicate via interrupts. Guests can read their VM ID from a device register (see ivshmem-spec.txt). +@subsubsection Migration with ivshmem + With device property @option{master=on}, the guest will copy the shared memory on migration to the destination host. With @option{master=off}, the guest will not be able to migrate with the device attached. In the latter case, the device should be detached and then reattached after migration using the PCI hotplug support. +At most one of the devices sharing the same memory can be master. The +master must complete migration before you plug back the other devices. + @subsubsection ivshmem and hugepages Instead of specifying the <shm size> using POSIX shm, you may specify
Migration with ivshmem needs to be carefully orchestrated to work. Exactly one peer (the "master") migrates to the destination, all other peers need to unplug (and disconnect), migrate, plug back (and reconnect). This is sort of documented in qemu-doc. If peers connect on the destination before migration completes, the shared memory can get messed up. This isn't documented anywhere. Fix that in qemu-doc. To avoid messing up register IVPosition on migration, the server must assign the same ID on source and destination. ivshmem-spec.txt leaves ID assignment unspecified, however. Amend ivshmem-spec.txt to require the first client to receive ID zero. The example ivshmem-server complies: it always assigns the first unused ID. For a bit of additional safety, enforce ID zero for the master. This does nothing when we're not using a server, because the ID is zero for all peers then. Signed-off-by: Markus Armbruster <armbru@redhat.com> --- docs/specs/ivshmem-spec.txt | 2 ++ hw/misc/ivshmem.c | 6 ++++++ qemu-doc.texi | 5 +++++ 3 files changed, 13 insertions(+)