Marking a physical page as uncacheable

Marking a physical page as uncacheable

[Timur Tabi]

How can I make a kernel-allocated page of memory uncacheable?  The ioremap()
function lets me specify a bitflag, so I know it's possible without using MTRR's.



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Re: Marking a physical page as uncacheable

[Mark Mokryn]

Try ioremap_nocache()

-Mark

Timur Tabi wrote:
> 
> How can I make a kernel-allocated page of memory uncacheable?  The ioremap()
> function lets me specify a bitflag, so I know it's possible without using MTRR's.
> 
> --
> Timur Tabi - ttabi@interactivesi.com
> Interactive Silicon - http://www.interactivesi.com
> 
> When replying to a mailing-list message, please don't cc: me, because then I'll just get two copies of the same message.
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
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Re: Marking a physical page as uncacheable

[Timur Tabi]

** Reply to message from Mark Mokryn <mark@sangate.com> on Thu, 20 Jul 2000
17:36:39 +0300


> Try ioremap_nocache()

That's just a front-end to __ioremap().  I'm trying to make REAL RAM as
uncacheable, not PCI memory.  ioremap() does not work on real RAM, only high
addresses outside of physical memory.



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Re: Marking a physical page as uncacheable

[Timur Tabi]

** Reply to message from Manfred Spraul <manfred@colorfullife.com> on Thu, 20
Jul 2000 18:16:56 +0200


> You could use ClearPageReserved() + ioremap(), but ioremap() is limited
> to the first 4 GB.

The 4GB limit is okay for now.

What does ClearPageReserved do?  Does it make the kernel think that the page is
part of high memory?  



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Re: Marking a physical page as uncacheable

[Manfred Spraul]

Timur Tabi wrote:
> 
> ** Reply to message from Mark Mokryn <mark@sangate.com> on Thu, 20 Jul 2000
> 17:36:39 +0300
> 
> > Try ioremap_nocache()
> 
> That's just a front-end to __ioremap().  I'm trying to make REAL RAM as
> uncacheable, not PCI memory.  ioremap() does not work on real RAM, only high
> addresses outside of physical memory.
> 

You could use ClearPageReserved() + ioremap(), but ioremap() is limited
to the first 4 GB.

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	Manfred
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Re: Marking a physical page as uncacheable

[Timur Tabi]

** Reply to message from Manfred Spraul <manfred@colorfullife.com> on Thu, 20
Jul 2000 18:16:56 +0200


> You could use ClearPageReserved() + ioremap(), but ioremap() is limited
> to the first 4 GB.

Is there an ioUNremap()?  I need to perform tests on the memory region with the
cache disabled.  If the tests don't reveal what I'm looking for, then I need to
unallocate the block.  



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Re: Marking a physical page as uncacheable

[Jeff Garzik]

On Thu, 20 Jul 2000, Timur Tabi wrote:
> ** Reply to message from Manfred Spraul <manfred@colorfullife.com> on Thu, 20
> Jul 2000 18:16:56 +0200
> > You could use ClearPageReserved() + ioremap(), but ioremap() is limited
> > to the first 4 GB.
> 
> Is there an ioUNremap()?  I need to perform tests on the memory region with the

It's called iounmap.  Please take a look at drivers which use the
functions are you interested in...  Also look at the docs :)
Documentation/IO-mapping.txt would be particularly helpful in this
instance.

	Jeff




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