On 09/16/2010 10:04 AM, Bjorn Helgaas wrote: > It does seem like we should do *something* with E820 reserved areas, but > I'm not 100% convinced we should be more strict than Windows. If we > pay attention to things Windows doesn't test, I think we're likely to > trip over even more BIOS bugs. Windows have a couple of advantages on us. They have WHQL; every machine needs to pass WHQL or it doesn't get sold. The other advantage is that most manufacturers of Windows desktops don't give a damn about anything other than the shipping configuration (Windows version and hardware): I have seen machines which fail to boot if you put in a PCI UART card. > Linux does avoid putting PCI devices in E820 reserved areas ... in > some cases. In this Dell case, the reserved area conflicts with a > host bridge window, so we expand the reserved area and insert it as > the *parent* of the window. Since it's the parent, it has no effect > on allocations from the window, so we end up putting devices in the > reserved area. OK, so that's a problem. This isn't really a hideously uncommon use case for a reserved region, either: it probably reflects a device used by SMM under that particular host bridge. > I think the problem is that E820 reservations fundamentally don't > fit well with the Linux resource manager. We manage resources as > a strict hierarchy of non-overlapping regions, but there's no > requirement that E820 reservations have any relationship with actual > devices that we discover via ACPI, PCI, etc. > > We've been kludging around this with a collection of hacks like > reserve_region_with_split() and insert_resource_expand_to_fit(), > but I think we're just making an unmaintainable mess. We should > take a step back and think about how to do this cleanly. Perhaps we should consider reserved regions a separate hierarchy, or we should deal with them at the time a new resource is created? -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
