* Re: how to tell linux (on x86) to ignore 1M or memory
[not found] ` <8c6EE-4Jj-5@gated-at.bofh.it>
@ 2007-04-20 21:39 ` Bodo Eggert
[not found] ` <8yGrK-4vX-7@gated-at.bofh.it>
1 sibling, 0 replies; 8+ messages in thread
From: Bodo Eggert @ 2007-04-20 21:39 UTC (permalink / raw)
To: Rene Herman, Dave Jones, Neil Brown, Andrew Morton,
Kyle McMartin, linux-kernel, alan, bcollins, pjones
Rene Herman <rene.herman@gmail.com> wrote:
> On 04/19/2007 04:18 PM, Bart Trojanowski wrote:
>> I need to preserve some state from the bios before entering protected
>> mode. For now I want to copy it into some ram accessible by real-mode,
>> say the last megabyte visible in real-mode.
>>
>> What's the easiest way to have linux ignore the megabyte starting at 15M?
>
> Note that real-mode can only access the first megabyte (*) and not the first
> 16. 16MB is the 16-bit protected mode (286) limit.
>
> (*) well, the first 1M + 64K - 16 bytes using segment FFFF assuming A20 is
> enabled and x > 1 in x86...
Interrupt 15h, function 87h allows copying from/to extended memory.
You might like to look into Ralph Brown's interrupt list for more details.
You could also cpio-gzip the data and append it to the initramfs.
--
Fun things to slip into your budget
Does that line item say 'Personal Massage System' Oops, it's supposed to be
'Message'. Go ahead and sign the authorization, Boss; I'll correct it later.
(Iike Hell I will)
^ permalink raw reply [flat|nested] 8+ messages in thread
[parent not found: <8yGrK-4vX-7@gated-at.bofh.it>]
* how to tell linux (on x86) to ignore 1M or memory
@ 2007-04-19 14:18 Bart Trojanowski
2007-04-19 14:30 ` Paolo Ornati
2007-04-20 19:01 ` Rene Herman
0 siblings, 2 replies; 8+ messages in thread
From: Bart Trojanowski @ 2007-04-19 14:18 UTC (permalink / raw)
To: linux-kernel
I need to preserve some state from the bios before entering protected
mode. For now I want to copy it into some ram accessible by real-mode,
say the last megabyte visible in real-mode.
What's the easiest way to have linux ignore the megabyte starting at 15M?
Cheers,
-Bart
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: how to tell linux (on x86) to ignore 1M or memory
2007-04-19 14:18 Bart Trojanowski
@ 2007-04-19 14:30 ` Paolo Ornati
2007-04-20 19:01 ` Rene Herman
1 sibling, 0 replies; 8+ messages in thread
From: Paolo Ornati @ 2007-04-19 14:30 UTC (permalink / raw)
To: Bart Trojanowski; +Cc: linux-kernel
On Thu, 19 Apr 2007 10:18:04 -0400
Bart Trojanowski <bart@jukie.net> wrote:
> I need to preserve some state from the bios before entering protected
> mode. For now I want to copy it into some ram accessible by real-mode,
> say the last megabyte visible in real-mode.
>
> What's the easiest way to have linux ignore the megabyte starting at 15M?
>
Documentation/kernel-parameters.txt:
memmap=nn[KMG]$ss[KMG]
[KNL,ACPI] Mark specific memory as reserved.
Region of memory to be used, from ss to ss+nn.
So adding this to kernel boot parameters should do the trick:
memmap=15M$1M
--
Paolo Ornati
Linux 2.6.21-rc7-CFS-v3-g6262cd9f on x86_64
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: how to tell linux (on x86) to ignore 1M or memory
2007-04-19 14:18 Bart Trojanowski
2007-04-19 14:30 ` Paolo Ornati
@ 2007-04-20 19:01 ` Rene Herman
2007-06-22 1:46 ` H. Peter Anvin
1 sibling, 1 reply; 8+ messages in thread
From: Rene Herman @ 2007-04-20 19:01 UTC (permalink / raw)
To: Bart Trojanowski; +Cc: linux-kernel
On 04/19/2007 04:18 PM, Bart Trojanowski wrote:
> I need to preserve some state from the bios before entering protected
> mode. For now I want to copy it into some ram accessible by real-mode,
> say the last megabyte visible in real-mode.
>
> What's the easiest way to have linux ignore the megabyte starting at 15M?
Note that real-mode can only access the first megabyte (*) and not the first
16. 16MB is the 16-bit protected mode (286) limit.
(*) well, the first 1M + 64K - 16 bytes using segment FFFF assuming A20 is
enabled and x > 1 in x86...
Rene.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: how to tell linux (on x86) to ignore 1M or memory
2007-04-20 19:01 ` Rene Herman
@ 2007-06-22 1:46 ` H. Peter Anvin
2007-06-22 13:16 ` Rene Herman
0 siblings, 1 reply; 8+ messages in thread
From: H. Peter Anvin @ 2007-06-22 1:46 UTC (permalink / raw)
To: Rene Herman; +Cc: Bart Trojanowski, linux-kernel
Rene Herman wrote:
> On 04/19/2007 04:18 PM, Bart Trojanowski wrote:
>
>> I need to preserve some state from the bios before entering protected
>> mode. For now I want to copy it into some ram accessible by
>> real-mode, say the last megabyte visible in real-mode.
>>
>> What's the easiest way to have linux ignore the megabyte starting at 15M?
>
> Note that real-mode can only access the first megabyte (*) and not the
> first 16. 16MB is the 16-bit protected mode (286) limit.
>
No, 16-bit protected mode (on 386+) is not limited to 16 MB.
The main reason there is a 16 MB limit in some current systems is that
ISA, and the ISA DMA controller only had 24 address lines.
-hpa
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: how to tell linux (on x86) to ignore 1M or memory
2007-06-22 1:46 ` H. Peter Anvin
@ 2007-06-22 13:16 ` Rene Herman
0 siblings, 0 replies; 8+ messages in thread
From: Rene Herman @ 2007-06-22 13:16 UTC (permalink / raw)
To: H. Peter Anvin; +Cc: Bart Trojanowski, linux-kernel
On 06/22/2007 03:46 AM, H. Peter Anvin wrote:
> Rene Herman wrote:
>> On 04/19/2007 04:18 PM, Bart Trojanowski wrote:
>>
>>> I need to preserve some state from the bios before entering protected
>>> mode. For now I want to copy it into some ram accessible by
>>> real-mode, say the last megabyte visible in real-mode.
>>>
>>> What's the easiest way to have linux ignore the megabyte starting at 15M?
>> Note that real-mode can only access the first megabyte (*) and not the
>> first 16. 16MB is the 16-bit protected mode (286) limit.
>>
>
> No, 16-bit protected mode (on 386+) is not limited to 16 MB.
That all depends on one's definition of 16-bit protected mode. The "(286)"
after mine meant I was talking about the definition in which descriptors
have a 24-bit base (and 16-bit limit) field -- ie, real 286 and arguably,
"real 16-bit protected mode".
Yes, I guess another valid definition is "code with a 16-bit address and
operand size default" on a 386+ and sure, that's just flipping a bit away.
In the context of Linux I agree it's also a sensible definition, so, well,
whatever. The point was that real mode could only access the first 1M, not
the first 16... :-)
Rene.
^ permalink raw reply [flat|nested] 8+ messages in thread
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[not found] <8bFEz-3B4-39@gated-at.bofh.it>
[not found] ` <8c6EE-4Jj-5@gated-at.bofh.it>
2007-04-20 21:39 ` how to tell linux (on x86) to ignore 1M or memory Bodo Eggert
[not found] ` <8yGrK-4vX-7@gated-at.bofh.it>
[not found] ` <8yRnb-4XE-23@gated-at.bofh.it>
2007-06-22 23:00 ` Bodo Eggert
2007-06-22 23:04 ` Rene Herman
2007-04-19 14:18 Bart Trojanowski
2007-04-19 14:30 ` Paolo Ornati
2007-04-20 19:01 ` Rene Herman
2007-06-22 1:46 ` H. Peter Anvin
2007-06-22 13:16 ` Rene Herman
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