Re: [PATCH] acpi: Bodge acpi_index migration

[Fabian Ebner]

Am 05.04.22 um 21:06 schrieb Dr. David Alan Gilbert (git):
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> The 'acpi_index' field is a statically configured field, which for
> some reason is migrated; this never makes much sense because it's
> command line static.
> 
> However, on piix4 it's conditional, and the condition/test function
> ends up having the wrong pointer passed to it (it gets a PIIX4PMState
> not the AcpiPciHpState it was expecting, because VMSTATE_PCI_HOTPLUG
> is a macro and not another struct).  This means the field is randomly
> loaded/saved based on a random pointer.  In 6.x this random pointer
> randomly seems to get 0 for everyone (!); in 7.0rc it's getting junk
> and trying to load a field that the source didn't send.  The migration
> stream gets out of line and hits the section footer.
> 
> The bodge is on piix4 never to load the field:
>   a) Most 6.x builds never send it, so most of the time the migration
>     will work.
>   b) We can backport this fix to 6.x to remove the boobytrap.
>   c) It should never have made a difference anyway since the acpi-index
>     is command line configured and should be correct on the destination
>     anyway
>   d) ich9 is still sending/receiving this (unconditionally all the time)
>     but due to (c) should never notice.  We could follow up to make it
>     skip.
> 
> It worries me just when (a) actually happens.
> 
> Fixes: b32bd76 ("pci: introduce acpi-index property for PCI device")
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/932
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  hw/acpi/acpi-pci-hotplug-stub.c |  4 ----
>  hw/acpi/pcihp.c                 |  6 ------
>  hw/acpi/piix4.c                 | 11 ++++++++++-
>  include/hw/acpi/pcihp.h         |  2 --
>  4 files changed, 10 insertions(+), 13 deletions(-)
> 

Fixes the issue for me, thanks!

Tested-by: Fabian Ebner <f.ebner@proxmox.com>