linux-kernel - Re: [PATCH] Fix e820 end address with EFI

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Date:	Mon, 02 Mar 2009 18:53:13 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Huang Ying <ying.huang@...el.com>
CC:	Brian Maly <bmaly@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fix e820 end address with EFI

Huang Ying wrote:
> On Tue, 2009-03-03 at 09:28 +0800, Yinghai Lu wrote:
>> Huang Ying wrote:
>>> On Tue, 2009-03-03 at 05:38 +0800, Yinghai Lu wrote:
>>>> Huang Ying wrote:
>>>>> On Mon, 2009-03-02 at 10:51 +0800, Yinghai Lu wrote:
>>>>>> On Sun, Mar 1, 2009 at 6:37 PM, Huang Ying <ying.huang@...el.com> wrote:
>>>>>>>> so 64bit could use ioremap_cache() too?
>>>>>>>> we may keep 32bit and 64bit a bit consistent.
>>>>>>> If we use ioremap_cache(), kexec runtime service will not work in kexec
>>>>>>> situation, which needs EFI runtime memory area to be mapped at exact
>>>>>>> same location across kexec. I think we should support kexec if possible.
>>>>>> sure.
>>>>>>
>>>>>> please don't touch max_low_pfn_mapped, because some range may not
>>>>>> directly mapped under those efi run-time code
>>>>> Find an issue to use init_memory_mapping() here.
>>>>>
>>>>> If the memory range to be mapped is less than 2M, the last mapped
>>>>> address may be next 2M aligned position, this may lead mapping
>>>>> overlapping between memory range. Such as:
>>>>>
>>>>> 0x3f388000 - 0x3f488000: real mapped	0x3f388000 - 0x3f600000
>>>>> 0x3f590000 - 0x3f5bb000: real mapped	0x3f590000 - 0x3f600000
>>>>>
>>>>> The problem is that the memory range 0x3f400000 - 0x3f590000 is left not
>>>>> mapped!
>>>> what is max_low_pfn_mapped before that?
>>> I don't know exactly what you mean. Can you elaborate a little?
>>>
>>> 0 ~ max_low_pfn_mapped ~ max_pfn_mapped can be mapped with
>>> init_memory_mapping() properly.
>>>
>>> The issue of above example is that 0x3f400000 ~ 0x3f488000 is a
>>> sub-range of 0x3f388000 ~ 0x3f488000, which should be mapped but is left
>>> not mapped.
>> what is max_low_pfn_mapped?
>>
>> what is init_memory_mapping() printout?
> 
> This does not comes from a real test case. To test the changes I made, I
> make efi_ioremap() being used even if the corresponding memory range is
> below max_low_pfn_mapped. The dmesg of test is attached with the mail.
> 
> The printout of init_memory_mapping shows:
> 
> init_memory_mapping: 000000003f488000-000000003f4bb000                          
> last_map_addr: 3f600000 end: 3f4bb000
> init_memory_mapping: 000000003f590000-000000003f5bb000                          
> last_map_addr: 3f600000 end: 3f5bb000
init_memory_mapping: 0000000000000000-000000003f700000                          

last_map_addr: 3f700000 end: 3f700000                                           

(6 early reservations) ==> bootmem [0000000000 - 003f700000]

so max_low_pfn_mapped is (3f700000>>12)
and you try to init_memory_mapping again before it

> init_memory_mapping: 00000000fffb0000-00000000fffba000                          
> last_map_addr: 100000000 end: fffba000
this one is interesting... got over mapped...
> 
> So I think it is possible to have the issue I mentioned above.

looks like.

YH
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