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

[Andreas Färber]

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.

Andreas

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