PCI: Restore detection of read-only BARs

commit 36e81648 upstream.

Commit 6ac665c6 ("PCI: rewrite PCI BAR reading code") masked off
low-order bits from 'l', but not from 'sz'.  Both are passed to pci_size(),
which compares 'base == maxbase' to check for read-only BARs.  The masking
of 'l' means that comparison will never be 'true', so the check for
read-only BARs no longer works.

Resolve this by also masking off the low-order bits of 'sz' before passing
it into pci_size() as 'maxbase'.  With this change, pci_size() will once
again catch the problems that have been encountered to date:

  - AGP aperture BAR of AMD-7xx host bridges: if the AGP window is
    disabled, this BAR is read-only and read as 0x00000008 [1]

  - BARs 0-4 of ALi IDE controllers can be non-zero and read-only [1]

  - Intel Sandy Bridge - Thermal Management Controller [8086:0103];
    BAR 0 returning 0xfed98004 [2]

  - Intel Xeon E5 v3/Core i7 Power Control Unit [8086:2fc0];
    Bar 0 returning 0x00001a [3]

Link: [1] https://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/commit/drivers/pci/probe.c?id=1307ef6621991f1c4bc3cec1b5a4ebd6fd3d66b9 ("PCI: probing read-only BARs" (pre-git))
Link: [2] https://bugzilla.kernel.org/show_bug.cgi?id=43331
Link: [3] https://bugzilla.kernel.org/show_bug.cgi?id=85991Reported-by: William Unruh <unruh@physics.ubc.ca>
Reported-by: Martin Lucina <martin@lucina.net>
Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/pci/probe.c

@@ -175,14 +175,17 @@ int __pci_read_base(struct pci_dev *dev, enum pci_bar_type type,
 		res->flags |= IORESOURCE_SIZEALIGN;
 		if (res->flags & IORESOURCE_IO) {
 			l &= PCI_BASE_ADDRESS_IO_MASK;
+			sz &= PCI_BASE_ADDRESS_IO_MASK;
 			mask = PCI_BASE_ADDRESS_IO_MASK & (u32) IO_SPACE_LIMIT;
 		} else {
 			l &= PCI_BASE_ADDRESS_MEM_MASK;
+			sz &= PCI_BASE_ADDRESS_MEM_MASK;
 			mask = (u32)PCI_BASE_ADDRESS_MEM_MASK;
 		}
 	} else {
 		res->flags |= (l & IORESOURCE_ROM_ENABLE);
 		l &= PCI_ROM_ADDRESS_MASK;
+		sz &= PCI_ROM_ADDRESS_MASK;
 		mask = (u32)PCI_ROM_ADDRESS_MASK;
 	}