Re: [RFC PATCH] PCI MMCONFIG: add validation against ACPI motherboard resources

Jesse Barnes
2007-05-24T00:05:53Z

On Sunday, April 29, 2007 7:14 pm Robert Hancock wrote:
> This path adds validation of the MMCONFIG table against the ACPI
> reserved motherboard resources. If the MMCONFIG table is found to be
> reserved in ACPI, we don't bother checking the E820 table. The PCI
> Express firmware spec apparently tells BIOS developers that
> reservation in ACPI is required and E820 reservation is optional, so
> checking against ACPI first makes sense. Many BIOSes don't reserve
> the MMCONFIG region in E820 even though it is perfectly functional,
> the existing check needlessly disables MMCONFIG in these cases.
>
> In order to do this, MMCONFIG setup has been split into two phases.
> If PCI configuration type 1 is not available (like on EFI Macs) then
> MMCONFIG is enabled early as before. Otherwise, it is enabled later
> after the ACPI interpreter is enabled, since we need to be able to
> execute control methods in order to check the ACPI reserved
> resources. Presently this is just triggered off the end of ACPI
> interpreter initialization.
>
> There are a few other behavioral changes here:
>
> -Validate all MMCONFIG configurations provided, not just the first
> one.
>
> -Validate the entire required length of each configuration according
> to the provided ending bus number is reserved, not just the minimum
> required allocation.
>
> -Validate that the area is reserved even if we read it from the
> chipset directly and not from the MCFG table. This catches the case
> where the BIOS didn't set the location properly in the chipset and
> has mapped it over other things it shouldn't have. This might be
> overly pessimistic - we might be able to instead verify that no other
> reserved resources (like chipset registers) are inside this memory
> range.
>
> Some testing is needed to see if this rejects MMCONFIG on all systems
> where it is problematic. There were some patches floating around to
> read the table location out of the chipset for Intel 915 and 965, I
> think the author found the latter to be problematic since the chipset
> had the table mapped over top of motherboard resources. The extra
> checking here may catch that case if we add that chipset-specific
> support.
>
> Applies to 2.6.21.1.
>
> Signed-off-by: Robert Hancock <hancockr@shaw.ca>

Acked-by: Jesse Barnes <jesse.barnes@intel.com>

As long as we get a fix for the mmconfig based probing issues in the
other thread, I think this patch should go in. Robert, maybe you could
submit it along with this one (and an i386 equivalent)? Type 1 config
access is already a fallback for mmconfig for x86_64 at least, so it
should be safe for non-extended access too, and it avoids problems with
our lack of decode disable in the generic PCI probing code.

Signed-off-by: Jesse Barnes <jesse.barnes@intel.com>

diff --git a/arch/x86_64/pci/mmconfig.c b/arch/x86_64/pci/mmconfig.c
index 65d8273..5052f80 100644
--- a/arch/x86_64/pci/mmconfig.c
+++ b/arch/x86_64/pci/mmconfig.c
@@ -61,7 +61,7 @@ static int pci_mmcfg_read(unsigned int seg, unsigned
int bus,
}

addr = pci_dev_base(seg, bus, devfn);
- if (!addr)
+ if (!addr || reg < 256) /* Use type 1 for non-extended access */
return pci_conf1_read(seg,bus,devfn,reg,len,value);

switch (len) {
@@ -89,7 +89,7 @@ static int pci_mmcfg_write(unsigned int seg, unsigned
int bus,
return -EINVAL;

addr = pci_dev_base(seg, bus, devfn);
- if (!addr)
+ if (!addr || reg < 256) /* Use type 1 for non-extended access */
return pci_conf1_write(seg,bus,devfn,reg,len,value);

switch (len) {