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


From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH 6/6] kvm: Fix dirty tracking with large kernel page size
Date: Sun, 4 Mar 2012 21:59:26 +0100


On 04.03.2012, at 21:31, Andreas Färber <address@hidden> wrote:

> 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. :)

Ugh. Sorry, apparently I can't read :). So you're saying 'break for ppcemb'. 
Hrm. Not sure that'd be all that great for 440, since there host pagesize is 
still 4k, but T_P_S is 1k.

Alex


> 
> Andreas
> 
> -- 
> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
> GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg



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