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Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg in
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS |
Date: |
Wed, 13 Nov 2013 13:04:10 +0100 |
On Wed, 13 Nov 2013 00:10:39 +0200
"Michael S. Tsirkin" <address@hidden> wrote:
> On Tue, Nov 12, 2013 at 07:26:02PM +0100, Paolo Bonzini wrote:
> > Il 12/11/2013 14:58, Igor Mammedov ha scritto:
> > > 'etc/reserved-memory-end' will allow QEMU to tell BIOS where PCI
> > > BARs mapping could safely start in high memory.
> > >
> > > Allowing BIOS to start mapping 64-bit PCI BARs at address where it
> > > wouldn't conflict with other mappings QEMU might place before it.
> > >
> > > That permits QEMU to reserve extra address space before
> > > 64-bit PCI hole for memory hotplug.
> >
> > I may be royally wrong, but I think the new file should only be added to
> > new machine types. Otherwise, after migrating old machine types from
> > new QEMU to old QEMU, you may end up with PCI BARs mapped outside the
> > "PCI windows" that exist until before patch 1/2 of this series.
> >
> > Does this make sense?
>
> Yes.
> Generally FW CFG must not be added/removed for a given machine types,
> otherwise guest that is migrated while reading it will
> get a corrupted result: half old and half new.
Is it true for a file 'etc/reserved-memory-end' though?
I've debugged SeaBIOS to learn more about it, and new->old migration with
following reboot, showed that file is not found by SeaBIOS (well since old
QEMU doesn't have it), as result SeaBIOS fallbacks to the old behavior
placing 64-PCI bars right above ram_over_4G as it was intended.
And with 'etc/reserved-memory-end' == ram_over_4G_end as it is in this
patch, there isn't issue whatsoever.
Looks like there is no migrations issues with files, provided SeaBIOS knows
how to deal with a missing file.
--
Regards,
Igor
- [Qemu-devel] [PATCH for-1.8 0/2 v3] pc: inform SeaBIOS where 64-bit PCI hole begins, Igor Mammedov, 2013/11/12
- [Qemu-devel] [PATCH 1/2] pc: map PCI address space as catchall region for not mapped addresses, Igor Mammedov, 2013/11/12
- [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS, Igor Mammedov, 2013/11/12
- Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS, Paolo Bonzini, 2013/11/12
- Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS, Igor Mammedov, 2013/11/12
- Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS, Michael S. Tsirkin, 2013/11/12
- Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS, Paolo Bonzini, 2013/11/12
- Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS,
Igor Mammedov <=
- Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS, Michael S. Tsirkin, 2013/11/14
- Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS, Igor Mammedov, 2013/11/14
- [Qemu-devel] [PATCH 2/2 v4] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS, Igor Mammedov, 2013/11/14