On Thu, Dec 16, 2010 at 9:38 AM, Bjorn Helgaas <bjorn.helgaas@xxxxxx> wrote: > > When we allocate address space, e.g., to assign it to a PCI device, don't > allocate anything mentioned in the BIOS E820 memory map. > > On recent machines (2008 and newer), we assign PCI resources from the > windows described by the ACPI PCI host bridge _CRS. On many Dell > machines, these windows overlap some E820 reserved areas, e.g., > > BIOS-e820: 00000000bfe4dc00 - 00000000c0000000 (reserved) > pci_root PNP0A03:00: host bridge window [mem 0xbff00000-0xdfffffff] > > If we put devices at 0xbff00000, they don't work, probably because > that's really RAM, not I/O memory. This patch prevents that by removing > the 0xbfe4dc00-0xbfffffff area from the "available" resource. > > I'm not very happy with this solution because Windows solves the problem > differently (it seems to ignore E820 reserved areas and it allocates > top-down instead of bottom-up; details at comment 45 of the bugzilla > below). That means we're vulnerable to BIOS defects that Windows would not > trip over. For example, if BIOS described a device in ACPI but didn't > mention it in E820, Windows would work fine but Linux would fail. > > Reference: https://bugzilla.kernel.org/show_bug.cgi?id=16228 > Signed-off-by: Bjorn Helgaas <bjorn.helgaas@xxxxxx> > --- > > arch/x86/kernel/resource.c | 38 +++++++++++++++++++++++++++++++++++++- > 1 files changed, 37 insertions(+), 1 deletions(-) > > > diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c > index 407a900..89638af 100644 > --- a/arch/x86/kernel/resource.c > +++ b/arch/x86/kernel/resource.c > @@ -1,11 +1,47 @@ > #include <linux/ioport.h> > #include <asm/e820.h> > > +static void resource_clip(struct resource *res, resource_size_t start, > + resource_size_t end) > +{ > + resource_size_t low = 0, high = 0; > + > + if (res->end < start || res->start > end) > + return; /* no conflict */ > + > + if (res->start < start) > + low = start - res->start; > + > + if (res->end > end) > + high = res->end - end; > + > + /* Keep the area above or below the conflict, whichever is larger */ > + if (low > high) > + res->end = start - 1; > + else > + res->start = end + 1; > +} > + > +static void remove_e820_regions(struct resource *avail) > +{ > + int i; > + struct e820entry *entry; > + > + for (i = 0; i < e820.nr_map; i++) { > + entry = &e820.map[i]; > + > + resource_clip(avail, entry->addr, > + entry->addr + entry->size - 1); > + } > +} > + > void arch_remove_reservations(struct resource *avail) > { > - /* Trim out BIOS area (low 1MB) */ > + /* Trim out BIOS area (low 1MB) and E820 regions */ > if (avail->flags & IORESOURCE_MEM) { > if (avail->start < BIOS_END) > avail->start = BIOS_END; > + > + remove_e820_regions(avail); > } > } that looks expensive. it will keep going through e820 tables... but e820 should have been reserved in resource tree... So why we need to check e820 again? Yinghai -- 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
