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.
+ if (RamSizeOver4G < (1LL << 40)) {
+ pci_mem64_top = 1LL << 44;
+ }
}
}
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