Re: [PATCH 3.2 015/152] PCI: Restore detection of read-only BARs

Bjorn Helgaas
2015-02-17T17:01:44Z

On Mon, Feb 16, 2015 at 7:46 PM, Ben Hutchings <ben@decadent.org.uk> wrote:
> 3.2.67-rc1 review patch. If anyone has any objections, please let me know.

No objections, but I think you want 06cf35f903aa ("PCI: Handle
read-only BARs on AMD CS553x devices") at the same time.

> ------------------
>
> From: Myron Stowe <myron.stowe@redhat.com>
>
> commit 36e8164882ca6d3c41cb91e6f09a3ed236841f80 upstream.
>
> Commit 6ac665c63dca ("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=85991
> Reported-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 | 3 +++
> 1 file changed, 3 insertions(+)
>
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -175,14 +175,17 @@ int __pci_read_base(struct pci_dev *dev,
> 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;
> }
>
>