From: Paolo Bonzini <pbonzini@redhat.com>
To: Ian Campbell <ijc@hellion.org.uk>, Gerd Hoffmann <kraxel@redhat.com>
Cc: Michael Tokarev <mjt@tls.msk.ru>, qemu-devel <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] 128Kb bios size and older machines?
Date: Fri, 07 Feb 2014 00:55:22 +0100 [thread overview]
Message-ID: <52F420EA.9000008@redhat.com> (raw)
In-Reply-To: <1391698125.25128.49.camel@kazak.uk.xensource.com>
Il 06/02/2014 15:48, Ian Campbell ha scritto:
>>> > > I'm not sure why the BIOS size is relevant to migration anyway, Xen
>>> > > doesn't load a new BIOS on the target host, the BIOS image is part of
>>> > > the migrated RAM.
>> >
>> > The memory layout is different with a larger bios as qemu makes the
>> > virtual flash as big as the bios image is. The different memory layout
>> > in turn makes live migration fail.
> OK. Xen doesn't emulate flash so it doesn't have this issue.
It's problematic even without flash. At least in Xen, all ROM memory
blocks are migrated, not just the main RAM. Migration of RAM/ROM block
data is independent from where the RAM/ROM is mapped in guest physical
address space.
In the guest, a 128k BIOS is at fffe0000-ffffffff.
A 256k BIOS is at fffc0000-ffffffff.
If the destination prepares the memory map for a 256k BIOS, and the
source sends the data for a 128k BIOS, the 128k BIOS is erroneously
placed at ffffc0000-fffdffff. There is no reset vector fffffff0. The
guest works fine until you reboot it, then it breaks.
Paolo
next prev parent reply other threads:[~2014-02-06 23:55 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-06 8:28 [Qemu-devel] 128Kb bios size and older machines? Michael Tokarev
2014-02-06 8:50 ` Gerd Hoffmann
2014-02-06 13:08 ` Michael Tokarev
2014-02-06 13:15 ` Ian Campbell
2014-02-06 13:30 ` Michael Tokarev
2014-02-06 13:52 ` Ian Campbell
2014-02-06 14:31 ` Gerd Hoffmann
2014-02-06 14:48 ` Ian Campbell
2014-02-06 23:55 ` Paolo Bonzini [this message]
2014-02-06 23:56 ` Paolo Bonzini
2014-02-07 7:11 ` Michael Tokarev
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