From: Avi Kivity <avi@redhat.com>
To: Stephen Donnelly <sfdonnelly@gmail.com>
Cc: kvm@vger.kernel.org, Cam Macdonell <cam@cs.ualberta.ca>
Subject: Re: R/W HG memory mappings with kvm?
Date: Mon, 06 Jul 2009 10:38:24 +0300 [thread overview]
Message-ID: <4A51A9F0.7000909@redhat.com> (raw)
In-Reply-To: <5f370d430907051541o752d3dbag80d5cb251e5e4d00@mail.gmail.com>
On 07/06/2009 01:41 AM, Stephen Donnelly wrote:
> I am looking at how to do memory mapped IO between host and guests
> under kvm. I expect to use the PCI emulation layer to present a PCI
> device to the guest.
>
> I see virtio_pci uses cpu_physical_memory_map() which provides either
> read or write mappings and notes "Use only for reads OR writes - not
> for read-modify-write operations."
>
Right, these are for unidirectional transient DMA.
> Is there an alternative method that allows large (Several MB)
> persistent hg memory mappings that are r/w? I would only be using this
> under kvm, not kqemu or plain qemu.
>
All of guest memory is permanently mapped in the host. You can use
accessors like cpu_physical_memory_rw() or cpu_physical_memory_map() to
access it. What exactly do you need that is not provided by these
accessors?
> Also it appears that PCI IO memory (cpu_register_io_memory) is
> provided via access functions, like the pci config space?
It can also use ordinary RAM (for example, vga maps its framebuffer as a
PCI BAR).
> Does this
> cause a page fault/vm_exit on each read or write, or is it more
> efficient than that?
>
It depends on how you configure it. Look at the vga code (hw/vga.c,
hw/cirrus_vga.c). Also Cam (copied) wrote a PCI card that provides
shared memory across guests, you may want to look at that.
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2009-07-06 7:36 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 [this message]
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 ` R/W HG memory mappings with kvm? Cam Macdonell
2009-07-27 21:32 ` 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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