On Fri, 21 Jun 2024 14:05:17 +0200
Gerd Hoffmann <kra...@redhat.com> wrote:
> On Wed, Jun 19, 2024 at 11:21:14AM GMT, John Levon wrote:
> > Older 32-bit Linux VMs (including Ubuntu 16.10) have issues with the
> > 64-bit pci io window, failing during boot with errors like:
>
> Well. Why people would use *that* ubuntu version is not clear to me.
> It's *loooooong* out of support. Even the LTS version from that year
> (16.04) is not supported any more. But it is at least available for
> download still, so I gave it a spin.
>
> Turns out it apparently can't deal with PCI bars mapped above 16TB (aka
> 44 phys-bits). Test patch below.
>
> take care,
> Gerd
>
> diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
> index bb44dc296047..a43876a931c9 100644
> --- a/src/fw/pciinit.c
> +++ b/src/fw/pciinit.c
> @@ -1189,11 +1189,16 @@ pci_setup(void)
>
> if (CPUPhysBits) {
> pci_mem64_top = 1LL << CPUPhysBits;
> - if (CPUPhysBits > 46) {
> - // Old linux kernels have trouble dealing with more than 46
> - // phys-bits, so avoid that for now. Seems to be a bug in the
> - // virtio-pci driver. Reported: centos-7, ubuntu-18.04
> - pci_mem64_top = 1LL << 46;
> + if (CPUPhysBits > 44) {
> + // Old linux kernels have trouble dealing with more than 44/46
> + // phys-bits. Seems to be a bug in the virtio-pci driver.
> + // 46: centos-7, ubuntu-18.04
> + // 44: ubuntu-16.04
> + // Limit the used address space to mitigate the bug, except we
> are
> + // running in a guest with more than 1TB of memory installed.
Is it possible to fix those broken drivers (centos-7 for example)
and ditch this heuristic altogether?
The rest of downstream can pick it up from there if they care about
their customers.
> + if (RamSizeOver4G < (1LL << 40)) {
> + pci_mem64_top = 1LL << 44;
> + }
> }
> }
>
>
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