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

[Andreas Färber]

Am 04.03.2012 21:25, schrieb 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! ;)

Exactly, which is why I'm saying just ignore the weird embedded case. :)

Andreas

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