On Thu, 26 Aug 2021 18:07:55 +0100,
Andre Przywara <[email protected]> wrote:
>
> On 8/25/21 6:44 PM, Marc Zyngier wrote:
>
> >> Actually, let me correct myself. I tested the wrong configuration (why
> >> isn't --force-pci the bloody default in kvmtool?).
>
> I guess because there is no --force-mmio, and PCI on ARM was kind of
> daunting back then ;-)
I remember that. But maybe we should change that default...
> >> Having dug further, it isn't the config space that causes problems,
> >> but the programming of the MSI-X vectors. I'm starting to suspect the
> >> layout of the MSI-X bar in kvmtool.
> >
> > OK, this is hilarious. Sort of. The MSI-X bar sizing is bonkers: you
> > can't fit 33 MSIs there (33 being the number of MSI-X that kvmtool
> > advertises), and you will have notionally overwritten the PBA as
> > well. Amusingly, the last write ends up being misdecoded as a config
> > space access...
>
> Ah, very good find indeed, many thanks for the debugging!
>
> I am only halfway through the code by now, but wouldn't you need to
> adjust the PBA offset in the MSIX capability as well? This is still
> stuck at that (misnamed) PCI_IO_SIZE, in
> virtio/pci.c:virtio_pci__init(): vpci->pci_hdr.msix.pba_offset =
> And IIUC this has to match the decoding in virtio_pci__msix_mmio_callback().
Indeed. I had this:
Region 2: Memory at 50000800 (32-bit, non-prefetchable) [size=1K]
Capabilities: [40] MSI-X: Enable+ Count=33 Masked-
Vector table: BAR=2 offset=00000000
PBA: BAR=2 offset=00000100
and with the PBA fix, I get:
Region 2: Memory at 50000800 (32-bit, non-prefetchable) [size=1K]
Capabilities: [40] MSI-X: Enable+ Count=33 Masked-
Vector table: BAR=2 offset=00000000
PBA: BAR=2 offset=00000210
which looks more sane. But man, this code is crufty as hell. I'll post
an updated patch later, once I've cleaned up a couple more things.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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