Re: [Qemu-devel] [PATCH 6/6] kvm: Fix dirty tracking with large kernel page size

[Alexander Graf]

On 04.03.2012, at 21:21, Andreas Färber <address@hidden> wrote:

> Am 04.03.2012 19:46, schrieb Alexander Graf:
>> 
>> 
>> On 04.03.2012, at 17:46, Andreas Färber <address@hidden> wrote:
>> 
>>> Am 04.03.2012 12:53, schrieb Benjamin Herrenschmidt:
>>>> On Sun, 2012-03-04 at 12:49 +0200, Avi Kivity wrote:
>>>>> On 02/28/2012 11:48 PM, Benjamin Herrenschmidt wrote:
>>>>>> On Tue, 2012-02-28 at 14:32 +0200, Avi Kivity wrote:
>>>>>> 
>>>>>>> What if TARGET_PAGE_SIZE > getpagesize()?  Or is that impossible?
>>>>>> 
>>>>>> We have yet to encounter such a case. It's not currently possible on
>>>>>> power (some old embedded chips could do 1K and 2K page sizes in the TLB
>>>>>> iirc but we never supported that in Linux and it's being phased out in
>>>>>> HW).
>>>>>> 
>>>>>> I suggest that gets dealt with when/if it needs to, which means probably
>>>>>> never :-)
>>>>> 
>>>>> Doesn't ppc support both 4k and 64k pages?  Suppose you run a 4k guest
>>>>> on a 64k host?
>>>>> 
>>>>> Maybe I'm misremembering or misunderstanding something.
>>> 
>>>> TARGET_PAGE_SIZE in qemu is always 4k for powerpc, it's a compile time
>>>> #define.
>>> 
>>> Except for ppcemb-softmmu (1k), which is irrelevant for KVM AFAIU.
>>> 
>>> Maybe just add an assert and be done with it?
>> 
>> Assert for what? Linux page size of 64k is something perfectly normal on 
>> ppc. The hardware can always do at least 4k maps however.
> 
> g_assert(TARGET_PAGE_SIZE <= getpagesize())
> 
> Just declare the above case as unsupported and abort if we encounter it.

What I'm trying to tell you is that it's the default case on book3s ppc! ;)

Alex