> Hi,
> There have been several machines that don't have a working MMCONFIG,
> often because of a buggy MCFG table in the ACPI bios. This patch adds a
> simple sanity check that detects a whole bunch of these cases, and when
> it detects it, linux now boots rather than crash-and-burns.
> [snip]
Arjan,
I am not sure if your analysis and your solution to the problem is correct.
It was my understanding that any memory NOT defined in the E820 tables
is NOT considered system memory. Therefore memory addresses defined in the
ACPI MCFG table do not have to show up in the E820 table.
Also the ACPI spec v3.0 (pg 405 of PDF, section 14.2, titled:
"E820 Assumptions and Limitations") agrees with this:
"The BIOS does not return a range description for the memory mapping
of PCI devices, ISA Option ROMs, and the ISA PNP cards because the OS
has mechanisms available to detect them."
(The ACPI v2.0c spec has this in section 15.2).
Obviously specifications are sometimes outdated, or assumptions are made in
some specifications which are not in other specification, so I was wondering
if you could tell me which specification defines that the memory addresses
in ACPI MCFG table have to be reserved in the E820 tables?
If this is not a specification issue, I was wondering if perhaps for the
machines you refer to, their BIOS bug is that the E820 have memory ranges
which also encompass what MMCONF points to?
Thanks!
Konrad Rzeszutek
IBM, (617)-693-1718
Konrad Rzeszutek wrote:
>> Hi,
>> There have been several machines that don't have a working MMCONFIG,
>> often because of a buggy MCFG table in the ACPI bios. This patch adds a
>> simple sanity check that detects a whole bunch of these cases, and when
>> it detects it, linux now boots rather than crash-and-burns.
>> [snip]
>
> Arjan,
>
> I am not sure if your analysis and your solution to the problem is correct.
> It was my understanding that any memory NOT defined in the E820 tables
> is NOT considered system memory. Therefore memory addresses defined in the
> ACPI MCFG table do not have to show up in the E820 table.
the problem is that Linux considers these 'free game' and will happily put
something like IO windows for cardbus cards there.
> Also the ACPI spec v3.0 (pg 405 of PDF, section 14.2, titled:
> "E820 Assumptions and Limitations") agrees with this:
>
> "The BIOS does not return a range description for the memory mapping
> of PCI devices, ISA Option ROMs, and the ISA PNP cards because the OS
> has mechanisms available to detect them."
MCFG is none of these...
> If this is not a specification issue, I was wondering if perhaps for the
> machines you refer to, their BIOS bug is that the E820 have memory ranges
> which also encompass what MMCONF points to?
no their bug is mostly that MCFG is garbage in those bioses. It points plain to
the wrong place. They even reserved the correct range, just pointed mcfg at the
wrong place.
On Thu, May 18, 2006 at 06:03:36AM -0700, Arjan van de Ven wrote:
> Konrad Rzeszutek wrote:
> >>Hi,
> >>There have been several machines that don't have a working MMCONFIG,
> >>often because of a buggy MCFG table in the ACPI bios. This patch adds a
> >>simple sanity check that detects a whole bunch of these cases, and when
> >>it detects it, linux now boots rather than crash-and-burns.
> >>[snip]
> >
> >Arjan,
> >
> >I am not sure if your analysis and your solution to the problem is
> >correct. It was my understanding that any memory NOT defined in the E820
> >tables is NOT considered system memory. Therefore memory addresses defined
> >in the ACPI MCFG table do not have to show up in the E820 table.
>
> the problem is that Linux considers these 'free game' and will happily put
> something like IO windows for cardbus cards there.
I can see this being a definite problem. I do not have machines with
ACPI MCFG and PCMCIA capability so I cannot reproduce this behavior.
Interestingly enough, somebody had a similar thought on their mind and
implemented a function 'clear_kernel_mapping' which, well, unmaps the
pages from the addresses that ACPI MCFG points to - so that it would not
be used as 'free game'.
This does not inhibit PCMCIA drivers from using other memory addresses
that are not in E820 and not in ACPI MCFG. However, those are reserved
during boot up (for example the EBDA). Also, the ACPI marks many memory
segments as reserved (which are not neccesarily marked reserved in
E820) to help the OS.
As I mentioned earlier, I do not have a machine with PCMCIA capability
and ACPI MCFG - but if you have access to such a machine, I would be
happy to look with you into creating a more comprehensive solution.
>
> >Also the ACPI spec v3.0 (pg 405 of PDF, section 14.2, titled:
> >"E820 Assumptions and Limitations") agrees with this:
> >
> >"The BIOS does not return a range description for the memory mapping
> >of PCI devices, ISA Option ROMs, and the ISA PNP cards because the OS
> >has mechanisms available to detect them."
>
> MCFG is none of these...
This is a bit of gray area. The end result of MCFG or 0xCF8/0xCFF is to
configure PCI devices and retrieve PCI memory mapped addresses (IO MMU).
0xCF8/0xCFF is limited in what it can do (only 256 bytes of
configuration date can be controlled), while MMCONFIG allows to
configure advanced features of the PCI-X and PCI Express (4KB of conf
data). Neither of these addresses - IO MMU or MCFG _has_ to show up in
the E820 tables.
Sometimes the IO MMU reserved memory shows up in the E820 as reserved.
The reason for this was to make life for the OS easier. Some OSes mark
256MB the IOMMU as reserved without bothering to check what is in there
(which can be done via querying the PCI devices and constructing a memory
table of PCI devices memory mapped addresses and how they fall in that
256MB).
The PCI Express and PCI-X configuration data can (but not always depending
on how much IOMMU the machine has set) be in the 256MB segment that the OS
reserves for IO MMU. The MMCONFIG is usually next to the start of IOMMU
memory address. On some machines that segment starts at 0xE0000000 and shows
up in the E820 tables as reserved. On other machines, this IOMMU segment is
in 0xF4000000, while MMCFG is in 0xF0000000 (64MB for MCFG, and 192MB for IOMMU).
And that memory segment (0xF0000000) does not show up in E820 table.
(FYI: No need to set up the full 256MB for MCFG as there isn't enought
PCI slots to need so much).
If the MMCONFIG falls in that assumed memory mapped 256MB - then
the quote from section 14.2 can apply to that particular situation
"The BIOS does not return a range for the memory mapping of PCI devices ...";
The end result is that the MCFG and IOMMU can point to memory ranges
reserved in E820, but do not neccesarily have to.
>
> >If this is not a specification issue, I was wondering if perhaps for the
> >machines you refer to, their BIOS bug is that the E820 have memory ranges
> >which also encompass what MMCONF points to?
>
> no their bug is mostly that MCFG is garbage in those bioses. It points
> plain to
> the wrong place. They even reserved the correct range, just pointed mcfg at
> the
> wrong place.
>
That is definitely a problem - and the "sanity-check" can definitly bail
out on those BIOSes and not crash Linux. The other side of the coin is that
BIOSes that do implement the MCFG/E820 correctly are penalized: the
MMCONFIG capability on those machines is turned off when using Linux
2.6.17.
Could you provide more details on the BIOS? Did the vendor released an updated BIOS?
Konrad Rzeszutek wrote:
>>> Also the ACPI spec v3.0 (pg 405 of PDF, section 14.2, titled:
>>> "E820 Assumptions and Limitations") agrees with this:
>>>
>>> "The BIOS does not return a range description for the memory mapping
>>> of PCI devices, ISA Option ROMs, and the ISA PNP cards because the OS
>>> has mechanisms available to detect them."
>> MCFG is none of these...
>
> This is a bit of gray area.
How? The segment you quoted basically says "no need to put any "MEM" resources
into E820 because the OS will know about those from its PCI scan".
And for an OS to map pci devices like cardbus or hotplug PCI anywhere, it obviously
needs to know about PCI so this is entirely a fair assumption.
MCFG is new. It's not traditional and it generally isn't a MEM region on any
PCI device. The result is that OSes that do not know about MCFG (like Windows XP)
do not at all know that there is something there already in the address space.
Neither the wording of the spec pieces you quoted nor common sense can lead to
a "but it doesn't have to be marked reserved" interpretation... the OS just has
to know what address space is free for mapping things into, via one way or another.
> If the MMCONFIG falls in that assumed memory mapped 256MB - then
> the quote from section 14.2 can apply to that particular situation
> "The BIOS does not return a range for the memory mapping of PCI devices ...";
yes this is the MEM BARs. Different animal.
>
>>> If this is not a specification issue, I was wondering if perhaps for the
>>> machines you refer to, their BIOS bug is that the E820 have memory ranges
>>> which also encompass what MMCONF points to?
>> no their bug is mostly that MCFG is garbage in those bioses. It points
>> plain to
>> the wrong place. They even reserved the correct range, just pointed mcfg at
>> the
>> wrong place.
>>
>
> That is definitely a problem - and the "sanity-check" can definitly bail
> out on those BIOSes and not crash Linux. The other side of the coin is that
> BIOSes that do implement the MCFG/E820 correctly are penalized:
I hereby contest that it's implemented correctly if it's not marked reserved...
> the
> MMCONFIG capability on those machines is turned off when using Linux
> 2.6.17.
>
> Could you provide more details on the BIOS? Did the vendor released an updated BIOS?
there were several, some I can't talk about.
Let me ask you a counter question: could you provide more details on the opposite case, and did the
vendor release an updated, fixed BIOS ?
Arjan van de Ven wrote:
> Konrad Rzeszutek wrote:
>
>> That is definitely a problem - and the "sanity-check" can definitly bail
>> out on those BIOSes and not crash Linux. The other side of the coin is
>> that BIOSes that do implement the MCFG/E820 correctly are penalized:
>
> I hereby contest that it's implemented correctly if it's not marked
> reserved...
PCI Firmware Specification 3.0
(http://www.pcisig.com/members/downloads/specifications/conventional/pcifw_r3.0.pdf),
page 42, notes for table 4-2, paragraph 2 says that firmware must report MCFG as
reserved region. Last sentence of same paragraph says that resources may be
optionally marked reserved by E820 or EFIGetMemoryMap, but must be always
reported as motherboard resources through ACPI (for exact citation please see
document itself, it is not freely available so I'm not going to copy-paste text
from it without written permission from pcisig...).
So it seems to me that BIOS not reporting MMCONFIG as reserved through E820 is
compliant, and what matters is that MMCONFIG must be reported as ACPI
motherboard resource.
Petr
Petr Vandrovec wrote:
> Arjan van de Ven wrote:
>> Konrad Rzeszutek wrote:
>>
>>> That is definitely a problem - and the "sanity-check" can definitly bail
>>> out on those BIOSes and not crash Linux. The other side of the coin
>>> is that BIOSes that do implement the MCFG/E820 correctly are penalized:
>>
>> I hereby contest that it's implemented correctly if it's not marked
>> reserved...
>
> PCI Firmware Specification 3.0
> (http://www.pcisig.com/members/downloads/specifications/conventional/pcifw_r3.0.pdf),
> page 42, notes for table 4-2, paragraph 2 says that firmware must report
> MCFG as reserved region. Last sentence of same paragraph says that
> resources may be optionally marked reserved by E820 or EFIGetMemoryMap,
resources == BARs, MCFG is a whole different beast
> but must be always reported as motherboard resources through ACPI (for
> exact citation please see document itself, it is not freely available so
> I'm not going to copy-paste text from it without written permission from
> pcisig...).
>
> So it seems to me that BIOS not reporting MMCONFIG as reserved through
> E820 is compliant, and what matters is that MMCONFIG must be reported as
> ACPI motherboard resource.
I think that's not the right interpretation; resources==BARs in this context.
I'll find a way to get that document and recheck to make sure...