From: Cam Macdonell <cam@cs.ualberta.ca>
To: Stephen Donnelly <sfdonnelly@gmail.com>
Cc: Avi Kivity <avi@redhat.com>,
"kvm@vger.kernel.org list" <kvm@vger.kernel.org>
Subject: Re: R/W HG memory mappings with kvm?
Date: Mon, 27 Jul 2009 08:48:52 -0600 [thread overview]
Message-ID: <4A6DBE54.3080609@cs.ualberta.ca> (raw)
In-Reply-To: <5f370d430907262256rd7f9fdalfbbec1f9492ce86@mail.gmail.com>
Stephen Donnelly wrote:
> Hi Cam,
Hi Steve,
Sorry I haven't answered your email from last Thursday. I'll answer it
shortly.
>
> On Thu, Jul 9, 2009 at 6:01 PM, Cam Macdonell<cam@cs.ualberta.ca> wrote:
>
>> The memory for the device allocated as a POSIX shared memory object and then
>> mmapped on to the allocated BAR region in Qemu's allocated memory. That's
>> actually one spot that needs a bit of fixing by passing the already
>> allocated memory object to qemu instead of mmapping on to it.
>
> If you work out how to use pre-existing host memory rather than
> allocating it inside qemu I would be interested.
How is the host memory pre-existing?
>
> I would like to have qemu mmap memory from a host char driver, and
> then in turn register that mapping as a PCI BAR for the guest device.
> (I know this sounds like pci pass-through, but it isn't.)
In my setup, qemu just calls mmap on the shared memory object that was
opened. So I *think* that switching the shm_open(...) to
open("/dev/chardev"), might be all that's necessary as long as your char
device handles mmapping.
> 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. Look at
qemu_ram_alloc() and qemu_get_ram_ptr() which are a two step process
that allocate the memory. Then notice that the ivshmem_ptr is mmapped
on to the memory that is returned from the qemu_get_ram_ptr.
pci_register_bar calls a function (the last parameter passed to it) that
in turn calls cpu_register_physical_memory which registers the allocated
memory (accessed a s->ivshmem_ptr) as the BAR.
Let me know if you have any more questions,
Cam
next prev parent reply other threads:[~2009-07-27 14:48 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-05 22:41 R/W HG memory mappings with kvm? Stephen Donnelly
2009-07-06 7:38 ` Avi Kivity
2009-07-07 22:23 ` Stephen Donnelly
2009-07-08 4:36 ` Avi Kivity
2009-07-08 21:33 ` Stephen Donnelly
2009-07-09 8:10 ` Avi Kivity
2009-07-08 21:45 ` Cam Macdonell
2009-07-08 22:01 ` Stephen Donnelly
2009-07-09 6:01 ` Cam Macdonell
2009-07-09 22:38 ` Stephen Donnelly
2009-07-10 17:03 ` Cam Macdonell
2009-07-12 21:28 ` Stephen Donnelly
2009-07-14 22:25 ` [PATCH] Support shared memory device PCI device Cam Macdonell
[not found] ` <5f370d430907262256rd7f9fdalfbbec1f9492ce86@mail.gmail.com>
2009-07-27 14:48 ` Cam Macdonell [this message]
2009-07-27 21:32 ` R/W HG memory mappings with kvm? Stephen Donnelly
2009-07-28 8:54 ` Avi Kivity
2009-07-28 23:06 ` Stephen Donnelly
2009-08-13 4:07 ` Stephen Donnelly
2009-08-19 12:14 ` Avi Kivity
2009-08-23 21:59 ` Stephen Donnelly
2009-08-24 4:55 ` Avi Kivity
2009-08-26 10:22 ` Avi Kivity
2009-08-27 2:39 ` Stephen Donnelly
2009-08-27 2:34 ` Stephen Donnelly
2009-08-27 4:08 ` Avi Kivity
2009-08-30 22:33 ` Stephen Donnelly
2009-08-31 8:44 ` Avi Kivity
2009-08-31 21:13 ` Stephen Donnelly
2009-09-09 12:50 ` Avi Kivity
2009-07-29 23:52 ` Cam Macdonell
2009-07-30 9:31 ` Avi Kivity
2009-09-28 18:27 Tsuyoshi Ozawa
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