Re: [PATCH v1 1/1] hw/pci: Disable PCI_ERR_UNCOR_MASK register for machine type < 8.0

[Fiona Ebner]

Am 03.05.23 um 02:27 schrieb Leonardo Bras:
> Since it's implementation on v8.0.0-rc0, having the PCI_ERR_UNCOR_MASK
> set for machine types < 8.0 will cause migration to fail if the target
> QEMU version is < 8.0.0 :
> 
> qemu-system-x86_64: get_pci_config_device: Bad config data: i=0x10a read: 40 
> device: 0 cmask: ff wmask: 0 w1cmask:0
> qemu-system-x86_64: Failed to load PCIDevice:config
> qemu-system-x86_64: Failed to load e1000e:parent_obj
> qemu-system-x86_64: error while loading state for instance 0x0 of device 
> '0000:00:02.0/e1000e'
> qemu-system-x86_64: load of migration failed: Invalid argument
> 
> The above test migrated a 7.2 machine type from QEMU master to QEMU 7.2.0,
> with this cmdline:
> 
> ./qemu-system-x86_64 -M pc-q35-7.2 [-incoming XXX]
> 
> In order to fix this, property x-pcie-err-unc-mask was introduced to
> control when PCI_ERR_UNCOR_MASK is enabled. This property is enabled by
> default, but is disabled if machine type <= 7.2.
> 
> Fixes: 010746ae1d ("hw/pci/aer: Implement PCI_ERR_UNCOR_MASK register")
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Leonardo Bras <leobras@redhat.com>

Thank you for the patch!

Closes: https://gitlab.com/qemu-project/qemu/-/issues/1576

AFAICT, this breaks (forward) migration from 8.0 to 8.0 + this patch
when using machine type <= 7.2. That is because after this patch, when
using machine type <= 7.2, the wmask for the register is not set and
when 8.0 sends a nonzero value for the register, the error condition in
get_pci_config_device() will trigger again.

Is it necessary to also handle that? Maybe by special casing the error
condition in get_pci_config_device() to be prepared to accept such a
stream from 8.0?

If that is considered not worth it, consider this:

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

Best Regards,
Fiona