linux-kernel - RE: [PATCH] x86: {reverve,free}_memtype() take a physical address

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Date:	Thu, 21 Aug 2008 15:57:35 -0700
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Rene Herman <rene.herman@...access.nl>
CC:	Ingo Molnar <mingo@...e.hu>, "Li, Shaohua" <shaohua.li@...el.com>,
	Dave Airlie <airlied@...il.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Arjan van de Ven <arjan@...radead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Dave Jones <davej@...emonkey.org.uk>
Subject: RE: [PATCH] x86: {reverve,free}_memtype() take a physical address



>-----Original Message-----
>From: Rene Herman [mailto:rene.herman@...access.nl]
>Sent: Thursday, August 21, 2008 3:27 PM
>To: Pallipadi, Venkatesh
>Cc: Ingo Molnar; Li, Shaohua; Dave Airlie; Yinghai Lu; Andreas
>Herrmann; Arjan van de Ven; Linux Kernel; Siddha, Suresh B;
>Thomas Gleixner; H. Peter Anvin; Dave Jones
>Subject: Re: [PATCH] x86: {reverve,free}_memtype() take a
>physical address
>
>On 22-08-08 00:16, Pallipadi, Venkatesh wrote:
>
>> Yes. Noticed that too and sent a patch here for x86/tip.
>>
>> http://www.ussg.iu.edu/hypermail/linux/kernel/0808.2/2270.html
>>
>> It is not very critical as it sounds as only set_memory_uc sets PAT
>> bits for RAM pages. Most other users (devmem mmap, ioramep, pci)
>> set PAT bits on the reserved memory. And there will not be conflicts
>> across RAM and reserveed regions. Regardless, this was a stupid
>> bug that we had missed earlier.
>
>And unfortunately I don't think the above fully fixes it for
>AGP. __pa()
>gets the real physical address and the memtypes should be on the GART
>remapped physical addresses it seems.
>

Page being marked here as uncached is the page got from alloc_page().
We are not really marking GART physical address as uncacheable. And
that page returned from alloc_page is what we are tracking with
reserve and free.
IOW, the tracking is only to keep CPU accesses consistent across
different va->pa and va across different CPUs and has nothing to do
with GART physical address here.

Thanks,
Venki
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