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Re: [PATCH v2] piix: fix regression during unplug in Xen HVM domUs
- To: Paolo Bonzini <pbonzini@xxxxxxxxxx>, John Snow <jsnow@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Olaf Hering <olaf@xxxxxxxxx>
- Date: Wed, 10 May 2023 09:47:19 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, qemu-devel@xxxxxxxxxx, qemu-block@xxxxxxxxxx, Philippe Mathieu-Daudé <f4bug@xxxxxxxxx>
- Delivery-date: Wed, 10 May 2023 07:48:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Wed, 10 May 2023 00:58:27 +0200 Olaf Hering <olaf@xxxxxxxxx>:
> In my debugging (with v8.0.0) it turned out the three pci_set_word
> causes the domU to hang. In fact, it is just the last one:
>
> pci_set_byte(pci_conf + 0x20, 0x01); /* BMIBA: 20-23h */
>
> It changes the value from 0xc121 to 0x1.
If I disable just "pci_set_word(pci_conf + PCI_COMMAND, 0x0000);" it works as
well.
It changes the value from 0x5 to 0.
In general I feel it is wrong to fiddle with PCI from the host side.
This is most likely not the intention of the Xen unplug protocol.
I'm sure the guest does not expect such changes under the hood.
It happens to work by luck with pvops kernels because their PCI discovery
is done after the unplug.
So, what do we do here to get this off the table?
Olaf
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