RE: [Xen-devel] Re: Paravirtualizing bits of acpi access

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Jeremy Fitzhardinge [mailto:jeremy@xxxxxxxx] 
>Sent: Tuesday, March 24, 2009 1:43 PM
>
>Tian, Kevin wrote:
>> The reason why those useless code are prevented, is in case of
>> clobberring 0-1M area which if contains valid Xen content. in
>> acpi_save_state_mem, dom0's wakeup code is copied to area
>> allocated in acpi_reserve_bootmem. If every Xen's usage on 0-1M
>> is based on copy-on-use style, such as trampoline code for AP
>> boot, it's ok. But I'm not sure whether Xen puts some persistent
>> content there. IIRC, that boot time allocation usually returns sth
>> like 0x90000 since wakeup stub is first run in real mode. But if
>> for dom0 alloc_bootmem_low never gives <1M page, then this
>> prevention could be skipped as your thought.
>>   
>
>Yes, but the memory allocated is only in 0-1M in dom0's 
>pseudo-physical 
>space, not in Xen's machine space.  It allocates the memory and does a 
>virt_to_phys on it, but there's no special effort to remap it 
>as mfns or 
>anything.  There should be no possible conflict with Xen's use of the 
>real 0-1M region.

OK, then it's safe to avoid that change. I had thought that dom0's 0-1M
is identity-mapped to machine 0-1M... :-)

Thanks,
Kevin

>
>Not that I've actually tried to execute that patch yet, so I 
>could well 
>be overlooking something...
>
>    J
>

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