On Fri, Jun 21, 2024 at 03:20:19PM GMT, Igor Mammedov wrote:
>
> > 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.
Some further testing showed that this is not version-specific but arch
specific. Old 32-bit kernels fail >44, old 64-bit kernels fail >46.
Note that 44 = 32 + 12, i.e. this could be pfn (page frame number)
hitting MAX_UINT32. Should that be the case the fix is probably not
easy (didn't check the kernel source though).
Also note that releasing a kernel fix is not enough, you also have to
respin install media. Distros which are *that* old typically don't get
regular install media updates any more ...
In short: The idea to fix distros and drop the heuristic is IMHO not
realistic.
take care,
Gerd
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