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From: "Pallipadi, Venkatesh" <email@example.com>
To: "Andi Kleen" <firstname.lastname@example.org>
Cc: <email@example.com>, <firstname.lastname@example.org>,
<email@example.com>, <firstname.lastname@example.org>, <email@example.com>,
"Siddha, Suresh B" <firstname.lastname@example.org>
Subject: RE: [patch 02/11] PAT x86: Map only usable memory in x86_64 identity map and kernel text
Date: Thu, 10 Jan 2008 12:50:55 -0800 [thread overview]
Message-ID: <924EFEDD5F540B4284297C4DC59F3DEE5A28CE@orsmsx423.amr.corp.intel.com> (raw)
>From: Andi Kleen [mailto:email@example.com]
>Sent: Thursday, January 10, 2008 11:28 AM
>To: Pallipadi, Venkatesh
>Cc: Andi Kleen; firstname.lastname@example.org; email@example.com;
>firstname.lastname@example.org; email@example.com; firstname.lastname@example.org;
>email@example.com; Siddha, Suresh B
>Subject: Re: [patch 02/11] PAT x86: Map only usable memory in
>x86_64 identity map and kernel text
>On Thu, Jan 10, 2008 at 11:17:07AM -0800, Pallipadi, Venkatesh wrote:
>> >I don't think that is needed or makes sense for
>reserved/ACPI * etc.
>> >Only e820 holes should be truly unmapped because only those should
>> >contain mmio.
>> Do you mean just the regions that are not listed in e820 at all? We
>> should also not map anything marked "RESERVED" in e820. Right?
>RESERVED is usually memory used by the BIOS. Properly MMIO areas
>should be in holes.
>Of course there might be buggy BIOS who violate that but the
>only way to find out is to check for the case in ioremap and
>warn. I would
>be still optimistic of it being correct.
>Another way would be to double check against the MTRRs - if
>it's UC then
>it should be unmapped. Maybe that would be a good idea. That should
>catch all true mmio holes unless a BIOS maps them cached but if it does
>that it's already beyond help.
One of the test systems I have has following E820
BIOS-e820: 0000000000000000 - 000000000009cc00 (usable)
BIOS-e820: 000000000009cc00 - 00000000000a0000 (reserved)
BIOS-e820: 00000000000cc000 - 00000000000d0000 (reserved)
BIOS-e820: 00000000000e4000 - 0000000000100000 (reserved)
BIOS-e820: 0000000000100000 - 00000000cff60000 (usable)
BIOS-e820: 00000000cff60000 - 00000000cff69000 (ACPI data)
BIOS-e820: 00000000cff69000 - 00000000cff80000 (ACPI NVS)
BIOS-e820: 00000000cff80000 - 00000000d0000000 (reserved)
BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)
BIOS-e820: 00000000fec00000 - 00000000fec10000 (reserved)
BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
BIOS-e820: 00000000ff000000 - 0000000100000000 (reserved)
BIOS-e820: 0000000100000000 - 0000000130000000 (usable)
I think it is unsafe to access any reserved areas through "WB" not just
mmio regions. In the above case 0xe0000000-0xf0000000 is one such
Also, relying on MTRR, is like giving more importance to BIOS writer
than required :-). I think the best way to deal with MTRR is just to not
touch it. Leave it as it is and do not try to assume that they are
correct, as frequently they will not be.
>> >> All reserved memory maps to a
>> >> zero page.
>> >Why zero page? Why not unmap.
>> I had it unmapped first. Then thought of zero mapping for dd
>> to continue working. May be there are apps that depend on that?
>> Also, dd of devmem seems to be already broken with big memory without
>> any of these changes.
>Exactly it's already broken.
>Anyways if someone accesses mmio through /dev/mem I think they
>want the real mappings, not a zero page. And dev/mem should provide.
>The trick is just to do it without caching attribute violations,
>but with mattr it is possible.
I don't like /dev/mem supporting access to mmio. We do not know what
attributes to use for these regions. We can potentially map all these
pages uncacheable. But there may be cases where reading an address can
block too possibly?
>> >Anyways you could make that a zillion times more simple by
>> >just rounding
>> >the e820 areas to 2MB -- for the holes only that should be
>ok I think;
>> >i would expect them to be near always already suitably aligned.
>> >In short this can be all done much simpler.
>> On systems I tested, ACPI regions are typically not 2MB
>aligned. And on
>ACPI regions don't need to be unmapped.
>> some systems there are few 4k pages of reserved holes just before
>reserved shouldn't be unmapped, just holes. Do they have holes
>there or reserved areas?
>I still hope 2MB alignment will work out.
E820 above has a combination of reserved and holes.
The problem is that we end up depending on specific e820s and paltform
specific problems/workarounds. This is not a real problem for i386 at
all, as we map only < 1G memory there. So, it is limited to x86_64
systems which should be less in number.
next prev parent reply other threads:[~2008-01-10 20:51 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-10 18:48 [patch 00/11] PAT x86: PAT support for x86 venkatesh.pallipadi
2008-01-10 18:48 ` [patch 01/11] PAT x86: Make acpi/other drivers map memory instead of assuming identity map venkatesh.pallipadi
2008-01-10 18:48 ` [patch 02/11] PAT x86: Map only usable memory in x86_64 identity map and kernel text venkatesh.pallipadi
2008-01-10 19:06 ` Andi Kleen
2008-01-10 19:17 ` Pallipadi, Venkatesh
2008-01-10 19:28 ` Andi Kleen
2008-01-10 20:50 ` Pallipadi, Venkatesh [this message]
2008-01-10 21:16 ` Andi Kleen
2008-01-10 22:25 ` Pallipadi, Venkatesh
2008-01-10 22:35 ` Andi Kleen
2008-01-14 16:43 ` Ingo Molnar
2008-01-14 21:21 ` Siddha, Suresh B
2008-01-14 21:28 ` Andi Kleen
2008-01-15 22:17 ` Ingo Molnar
2008-01-15 23:11 ` Andi Kleen
2008-01-15 23:21 ` Siddha, Suresh B
2008-01-18 12:01 ` Ingo Molnar
2008-01-18 13:12 ` Andi Kleen
2008-01-18 16:46 ` Jesse Barnes
2008-01-18 18:12 ` Andi Kleen
2008-01-18 19:02 ` Jesse Barnes
2008-01-19 2:42 ` Andi Kleen
2008-01-10 21:05 ` Linus Torvalds
2008-01-10 21:57 ` Pallipadi, Venkatesh
2008-01-10 22:15 ` Linus Torvalds
2008-01-10 22:27 ` Pallipadi, Venkatesh
2008-01-10 22:50 ` Valdis.Kletnieks
2008-01-18 18:27 ` Dave Jones
2008-01-18 20:54 ` Ingo Molnar
2008-01-10 18:48 ` [patch 03/11] PAT x86: Map only usable memory in i386 identity map venkatesh.pallipadi
2008-01-10 19:10 ` Andi Kleen
2008-01-10 18:48 ` [patch 04/11] PAT x86: Basic PAT implementation venkatesh.pallipadi
2008-01-10 18:48 ` [patch 05/11] PAT x86: drm driver changes for PAT venkatesh.pallipadi
2008-01-10 18:48 ` [patch 06/11] PAT x86: Refactoring i386 cpa venkatesh.pallipadi
2008-01-10 19:00 ` Andi Kleen
2008-01-14 16:47 ` Ingo Molnar
2008-01-10 18:48 ` [patch 07/11] PAT x86: pat-conflict resolution using linear list venkatesh.pallipadi
2008-01-10 19:13 ` Andi Kleen
2008-01-10 20:08 ` Pallipadi, Venkatesh
2008-01-10 18:48 ` [patch 08/11] PAT x86: pci mmap conlfict patch venkatesh.pallipadi
2008-01-10 18:48 ` [patch 09/11] PAT x86: Add ioremap_wc support venkatesh.pallipadi
2008-01-10 19:08 ` Andi Kleen
2008-01-10 19:25 ` Pallipadi, Venkatesh
2008-01-12 0:18 ` Roland Dreier
2008-01-10 18:48 ` [patch 10/11] PAT x86: Handle /dev/mem mappings venkatesh.pallipadi
2008-01-10 18:48 ` [patch 11/11] PAT x86: Expose uc and wc interfaces in /sysfs vor pci_mmap_resource venkatesh.pallipadi
2008-01-10 19:43 ` Greg KH
2008-01-10 20:54 ` [patch 11/11] PAT x86: Expose uc and wc interfaces in /sysfsvor pci_mmap_resource Pallipadi, Venkatesh
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