Re: [Qemu-devel] [PATCH] map 64-bit PCI BARs at location provided by emulator

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 11 Oct 2013 14:35:50 +0200
Gerd Hoffmann <kraxel@redhat.com> wrote:

> On Fr, 2013-10-11 at 12:19 +0200, Igor Mammedov wrote:
> > Currently 64-bit PCI BARs are unconditionally mapped by BIOS right
> > over 4G + RamSizeOver4G location, which doesn't allow to reserve
> > extra space before 64-bit PCI window. For memory hotplug an extra
> > RAM space might be reserved after present 64-bit RAM end and BIOS
> > should map 64-bit PCI BARs after it.
> > 
> > Introduce "etc/pcimem64-start" romfile to provide BIOS a hint
> > where it should start mapping of 64-bit PCI BARs. If romfile is
> > missing BIOS reverts to legacy behavior and starts mapping right
> > after high memory.
> 
> Looks good overall.
> 
> 
> >          struct pci_region r64_mem, r64_pref;
> > +        u64 base64 = le64_to_cpu(romfile_loadint("etc/pcimem64-start",
> > +                                 0x100000000ULL + RamSizeOver4G));
> 
> Should we sanity-check base64 maybe?
> Make sure it isn't smaller than 0x100000000ULL + RamSizeOver4G?
If it would be less than 0x100000000ULL + RamSizeOver4G then it would mean
that QEMU for some reason decided to overshadow present RAM with PCI hole.

It would add a couple of extra bytes to BIOS and point where it should fail
or at least print a warning that nobody will read at runtime.
I think it's better to assert on QEMU side and abort even before guest
started if it's considered as error.

> 
> cheers,
>   Gerd
>        
> 
>