linux-kernel - [PATCH 1/5] PCI: Don't check resource_size() in pci_bus_alloc

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Message-ID: <20140311174243.23084.77689.stgit@bhelgaas-glaptop.roam.corp.google.com>
Date:	Tue, 11 Mar 2014 11:42:43 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	linux-pci@...r.kernel.org
Cc:	Paul Bolle <pebolle@...cali.nl>, Yinghai Lu <yinghai@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/5] PCI: Don't check resource_size() in
 pci_bus_alloc_resource()

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@...cali.nl>
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
---
 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

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