linux-kernel - Re: [PATCH] x86/PCI: never allocate PCI MMIO resources below BIOS

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Date:	Mon, 26 Apr 2010 14:59:49 -0700
From:	Yinghai Lu <yinghai.lu@...cle.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Andy Isaacson <adi@...apodia.org>,
	"R. Andrew Bailey" <bailey@...mai.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, guenter.roeck@...csson.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Renninger <trenn@...e.de>, yaneti@...lera.com
Subject: Re: [PATCH] x86/PCI: never allocate PCI MMIO resources below  BIOS_END

On 04/26/2010 02:25 PM, Jesse Barnes wrote:
> On Mon, 26 Apr 2010 14:12:35 -0700
> "H. Peter Anvin" <hpa@...or.com> wrote:
>
>   
>>> On Mon, 26 Apr 2010 14:27:56 -0600
>>> Bjorn Helgaas <bjorn.helgaas@...com> wrote:
>>>       
>>>> I'm a little concerned that those patches are a sledgehammer approach.
>>>> Previously, IORESOURCE_BUSY has basically been used for mutual exclusion
>>>> between drivers that would otherwise claim the same resource.  It hasn't
>>>> been used to guide resource assignment in the PCI/PNP/etc core.  Maybe
>>>> it's a good idea to also use IORESOURCE_BUSY there, but I'm not sure.
>>>> Right now it feels like undesirable overloading to me.
>>>>         
>>> I guess that's true, removing those regions from the pool entirely
>>> might be better?  Or some other, clear way of expressing that the
>>> regions aren't available to drivers.  Maybe we need a new IO resource
>>> type for platform ranges.
>>>
>>>       
>>>> I think it also leads to at least one problem: Guenter's machine has no
>>>> VGA but has a PCI device that lives at 0xa0000.  The driver for that
>>>> device won't be able to request that region if the arch code has marked
>>>> it busy.
>>>>         
>>> Ah good point, so we'll want another approach at any rate.  Yinghai?
>>>       
>> What we need is to keep track of the areas available for address space
>> allocation by dynamically addressed devices, as distinct from address
>> space that is in use by a kernel-known device.  There is an in-between,
>> which one can call "here there be dragons" space, which should never be
>> used for dynamic device allocation, but if a platform device or
>> pre-assigned device uses that space then it should be allowed to be
>> allocated.
>>
>> In the case of x86, anything that is E820_RESERVED, *or* in the legacy
>> region (below 1 MB) and is not RAM, is "here there be dragons" space.
>>     
> Agreed.  The trickier part is handling any platform devices that
> request_resource against that space.  But maybe we don't need to do
> anything special; just making sure we avoid it in the PCI "BIOS" code
> as Bjorn did may be sufficient.
>
>   

the two regressions from the reporters:

BIOS put 0xa0000-0xb0000, 0xc0000- 0xd0000 with E820_RESERVED.
BIOS ACPI _CRS keep 0xa0000-0xb0000, 0xc0000-0xd0000 as part resources
for peer root bus: BUS 0.

kernel insert 0xa0000-0xb0000 into resource tree with _BUSY in
e820_reserve_resources() at first.
last pci bus scan code, will insert 0xa0000-0xb0000, and it is under
previous reserved entry.

later pci_assign_unassign code, will use bus 0 resources directly, and
don't care if the parent's have _BUSY bit.

solutions:
1. mark _BUSY under bus 0 resource:  ==> -v3
2. split e820 reserve entries to small pieces to fit into bus 0
resources, so will have holder under bus0 resources. it will prevent
those range to be used.
   -v4
3. reject any dynamically allocation under 1M.  ==> Bjorn's new patch.

till now, driver can reserve resource under 1M, only when those range is
not in e820.

case A:
bus 0: --- bus X --- device Y
if the BIOS only assign range to to BUS X bridge with 0xB0000, and
device Y is not assigned.  then with Bojorn's patch, device Y can not
get right resource allocated on first try.

my -v4 can handle that case.

YH
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