Re: [PATCH 1/5] PCI: Don't check resource_size() in pci_bus_alloc_resource()

[Yinghai Lu]

On Tue, Mar 11, 2014 at 10:42 AM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> Paul reported that after f75b99d5a77d ("PCI: Enforce bus address limits in
> resource allocation") on a 32-bit kernel (CONFIG_PHYS_ADDR_T_64BIT not
> set), intel-gtt complained "can't ioremap flush page - no chipset
> flushing".  In addition, other PCI resource allocations, e.g., for bridge
> windows, failed.
>
> This happens because we incorrectly skip bus resources of
> [mem 0x00000000-0xffffffff] because we think they are of size zero.
> When resource_size_t is 32 bits wide, resource_size() on
> [mem 0x00000000-0xffffffff] returns 0 because (r->end - r->start + 1)
> overflows.
>
> Therefore, we can't use "resource_size() == 0" to decide that allocation
> from this resource will fail.  allocate_resource() should fail anyway if it
> can't satisfy the address constraints, so we should just depend on that.
>
> A [mem 0x00000000-0xffffffff] bus resource is obviously not really valid,
> but we do fall back to it as a default when we don't have information about
> host bridge apertures.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=71611
> Fixes: f75b99d5a77d PCI: Enforce bus address limits in resource allocation
> Reported-and-tested-by: Paul Bolle <pebolle@xxxxxxxxxx>
> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> ---
>  drivers/pci/bus.c |    2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 00660cc502c5..38901665c770 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -162,8 +162,6 @@ static int pci_bus_alloc_from_region(struct pci_bus *bus, struct resource *res,
>
>                 avail = *r;
>                 pci_clip_resource_to_region(bus, &avail, region);
> -               if (!resource_size(&avail))
> -                       continue;
>
>                 /*
>                  * "min" is typically PCIBIOS_MIN_IO or PCIBIOS_MIN_MEM to
>

how about replacing that with:

        if (avail.start > avail.end)
                  continue;

so we do not need to go deep into allocate_resource()

Thanks

Yinghai
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