From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jan Kiszka <jan.kiszka@siemens.com>
Subject: Re: Heads up: More user-unaccessible x86 states?
Date: Mon, 05 Oct 2009 14:42:18 +0200
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Cc: kvm-devel <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
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Avi Kivity wrote:
> On 10/05/2009 02:18 PM, Jan Kiszka wrote:
>>> True pointers are no go since we have to deal with compat code (31/32
>>> bit userspace calling into a 64 bit kernel).  Offsets into the state
>>> structure are easier.
>>>      
>> So current KVM_GET_DIRTY_LOG is broken in the compat case...
>>
>>    
> 
> Yes, for big-endian 32/64 and s390.  There are some patches floating around.

Well, that's for fixing up the endianess of the bitmap itself. But the
problem with void * in compat code are their different sizes. And
GET_DIRTY_LOG solves this via padding:

	union {
		void __user *dirty_bitmap;
		__u64 padding2;
	};

So this should not make pointers a no-go, should it?

> 
>> We'll probably have to deal with both. Therefore, I'm looking for a
>> unified solution.
>>
>>    
> 
> array of
> 
> struct {
>     __u16 type;
>     __u16 offset;
> } ?
> 

For sure possible, just the setup of such data structure in user space
gets a bit, well, unhandy.

Jan

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