From: Cam Macdonell <cam@cs.ualberta.ca>
To: Avi Kivity <avi@redhat.com>
Cc: Stephen Donnelly <sfdonnelly@gmail.com>, kvm@vger.kernel.org
Subject: Re: R/W HG memory mappings with kvm?
Date: Wed, 08 Jul 2009 15:45:43 -0600 [thread overview]
Message-ID: <4A551387.3000702@cs.ualberta.ca> (raw)
In-Reply-To: <4A54225F.1050703@redhat.com>
Avi Kivity wrote:
> On 07/08/2009 01:23 AM, Stephen Donnelly wrote:
>>
>>>> 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).
>>>
>>
>> So host memory is exported as a PCI_BAR to the guest via
>> cpu_register_physical_memory(). It looks like the code has to
>> explicitly manage marking pages dirty and synchronising at appropriate
>> times. Is the coherency problem bidirectional, e.g. writes from either
>> host or guest to the shared memory need to mark pages dirty, and
>> ensure sync is called before the other side reads those areas?
>>
>
> Shared memory is fully coherent. You can use the ordinary x86 bus lock
> operations for concurrent read-modify-write access, and the memory
> barrier instructions to prevent reordering. Just like ordinary shared
> memory.
>
>>>> 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.
>>>
>>
>> I will look into the vga code and see if I get inspired. The 'copied'
>> driver sounds interesting, the code is not in kvm git?
>>
>
> (copied) means Cam was copied (cc'ed) on the email, not the name of the
> driver. It hasn't been merged but copies (of the driver, not Cam) are
> floating around on the Internet.
Hi Stephen,
Here is the latest patch that supports interrupts. I am currently
working on a broadcast mechanism that should be ready fairly soon.
http://patchwork.kernel.org/patch/22368/
I have some test scripts that can demonstrate how to use the memory
between guest/host and guest/guest. Let me know if you would like me to
send them to you.
Cheers,
Cam
>
> The relevant parts of cirrus_vga.c are:
>
> static void cirrus_pci_lfb_map(PCIDevice *d, int region_num,
> uint32_t addr, uint32_t size, int type)
> {
>
> ...
>
> /* XXX: add byte swapping apertures */
> cpu_register_physical_memory(addr, s->vga.vram_size,
> s->cirrus_linear_io_addr);
>
> This function is called whenever the guest updates the BAR.
>
next prev parent reply other threads:[~2009-07-08 22:16 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 [this message]
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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