linux-kernel - Re: another pagetable initialization crash on xen

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Message-ID: <4D936F2D.4000902@kernel.org>
Date:	Wed, 30 Mar 2011 10:58:05 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: another pagetable initialization crash on xen

On 03/30/2011 09:59 AM, Stefano Stabellini wrote:
> On Wed, 30 Mar 2011, Stefano Stabellini wrote:
>> I have another unrelated question: init_memory_mapping is called on the
>> range 0 - max_low_pfn, but that range usually includes a reserved region
>> below the first MB. On one machine of mine the IOAPIC mmio region falls
>> in that memory range therefore we are mapping the IOAPIC mmio region in
>> init_memory_mapping without going through the fixmap as we should.
>> This is causing problems on Xen, but I guess it could theoretically
>> cause problems on other platforms as well. Should we avoid reserved
>> memory regions below the first MB from the initial memory mappings?
>
> Sorry I mixed up frame numbers with physical addresses, so the IOAPIC
> mmio region is actually at 0xfec00000 where it should be but it gets
> mapped during the initial memory mapping (range 0 - 0x100000000).
> Is that supposed to happen? Shouldn't it go through the fixmap?

io apic addr is going through fixmap.

initial_memory_mapping will map to [0, max_mem_under_4g).
max_mem_under_4g is from E820 table searching.

later it will map [4g, max_mem_above_4g).

We do not map mmio gap between [max_mem_under_4g,4g)

Thanks

Yinghai
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