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Date: Mon, 15 Sep 2008 10:08:24 -0300
From: Glauber Costa <glommer@redhat.com>
Subject: Re: [Qemu-devel] Re: [PATCH] Make page_find() return 0 for
	too-large addresses
Message-ID: <20080915130824.GA6066@poweredge.glommer>
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: gcosta@redhat.com, Eduardo Habkost <ehabkost@redhat.com>, kvm@vger.kernel.org, qemu-devel@nongnu.org

On Fri, Sep 12, 2008 at 04:27:30PM -0500, Anthony Liguori wrote:
> Eduardo Habkost wrote:
>> On Fri, Sep 12, 2008 at 05:14:06PM -0300, Eduardo Habkost wrote:
>>   
>>> On Fri, Sep 12, 2008 at 02:50:33PM -0500, Anthony Liguori wrote:
>>>     
>>>> Eduardo Habkost wrote:
>>>>       
>>>>> On some cases, such as under KVM, tb_invalidate_phys_page_range()
>>>>> may be called for large addresses, when qemu is configured to more than
>>>>> 4GB of RAM.
>>>>>
>>>>> On these cases, qemu was crashing because it was using an index too
>>>>> large for l1_map[], that supports only 32-bit addresses when compiling
>>>>> without CONFIG_USER_ONLY.
>>>>>           
>> <snip>
>>   
>
> So... are you building with kqemu enabled?  If so,  
> TARGET_PHYS_ADDR_SPACE_BITS will be 32.  So I don't think this sort of  
> work-around is correct.  A better solution would be to validate ram_size  
> against TARGET_PHYS_ADDR_SPACE_BITS.
>
> To put it another way, if you have kqemu enabled (at build time), you  
> cannot use > ~4GB of memory for the guest.
I can be very wrong here, but page_find() does not seem to limit our ability to
run guests if > 4GB, as it is only concerned about the code translation layer.
Differently from phys_page_find(), that does manage physical memory, and even
presented problems about it in the past.

>
> Regards,
>
> Anthony Liguori
>