Re: R/W HG memory mappings with kvm?

From: Avi Kivity <avi@redhat.com>
To: Stephen Donnelly <sfdonnelly@gmail.com>
Cc: Cam Macdonell <cam@cs.ualberta.ca>,
	"kvm@vger.kernel.org list" <kvm@vger.kernel.org>
Subject: Re: R/W HG memory mappings with kvm?
Date: Tue, 28 Jul 2009 11:54:11 +0300	[thread overview]
Message-ID: <4A6EBCB3.4080804@redhat.com> (raw)
In-Reply-To: <5f370d430907271432y5283c2cat7673efeed0febe20@mail.gmail.com>

On 07/28/2009 12:32 AM, Stephen Donnelly wrote:
>>> What I don't understand is how to turn the host address returned from
>>> mmap into a ram_addr_t to pass to pci_register_bar.
>>>        
>> Memory must be allocated using the qemu RAM functions.
>>      
>
> That seems to be the problem. The memory cannot be allocated by
> qemu_ram_alloc, because it is coming from the mmap call. The memory is
> already allocated outside the qemu process. mmap can indicate where in
> the qemu process address space the local mapping should be, but
> mapping it 'on top' of memory allocated with qemu_ram_alloc doesn't
> seem to work (I get a BUG in gfn_to_pfn).
>    

You need a variant of qemu_ram_alloc() that accepts an fd and offset and 
mmaps that.  A less intrusive, but uglier, alternative is to call 
qemu_ram_alloc() and them mmap(MAP_FIXED) on top of that.

-- 
error compiling committee.c: too many arguments to function