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Re: [Qemu-devel] Virtual Machine Generation ID
From: |
Ben Warren |
Subject: |
Re: [Qemu-devel] Virtual Machine Generation ID |
Date: |
Sat, 14 Jan 2017 22:17:53 -0800 |
Hi Michael,
> On Dec 10, 2016, at 7:28 PM, Michael S. Tsirkin <address@hidden> wrote:
>
> On Tue, Dec 06, 2016 at 06:15:34PM -0800, Ben Warren wrote:
>> Hi Michael,
>>
>> I’m well on my way to implementing this, but I am really new to the QEMU
>> code base and am struggling with some concepts. Please see below:
>>> On Oct 5, 2016, at 6:29 PM, Michael S. Tsirkin <address@hidden> wrote:
>>>
>>> On Tue, Oct 04, 2016 at 03:51:40PM -0700, Ed Swierk wrote:
>>>> On Thu, Sep 15, 2016 at 5:36 PM, Michael S. Tsirkin <address@hidden> wrote:
>>>>> On Thu, Sep 15, 2016 at 05:23:28PM -0700, Ed Swierk wrote:
>>>>>> I'm wondering what it will take to finish up work on vmgenid.
>>>>>>
>>>>>> https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg05599.html
>>>>>
>>>>> We have ACPI_BUILD_TPMLOG_FILE in tree now and I think it could be
>>>>> allocated in a similar way.
>>>>> Integrate patch "fw-cfg: support writeable blobs" to communicate the
>>>>> allocated address back to QEMU.
>>>>
>>>> Starting with Igor's last version at
>>>> https://github.com/imammedo/qemu/commits/vmgen_wip , it's not clear to
>>>> me which changes need to be ported, which changes are obsoleted by
>>>> your new fw-cfg stuff and/or upstream churn in ACPI, device
>>>> properties, etc. In particular ACPI is still a total mystery to me,
>>>> though passing a single address from guest to host can't be that hard,
>>>> can it?
>>>>
>>>> Any clues would be appreciated.
>>>>
>>>> --Ed
>>>
>>> It might be best to just re-start from the beginning.
>>> So the idea is that ACPI should be about supplying the address
>>> to guest. To supply address to host we'll use fw cfg.
>>> This would be new I think:
>>>
>>> - add support for writeable fw cfg blobs
>> patch applied
>>> - add linker/loader command to write address of a blob into
>>> such a fw cfg file
>>> - add a new file used for vm gen id, use loader command above
>>> to pass the address of a blob allocated for it to host
>> I don’t really understand the meaning of “file” in this context. It seems
>> to be a way of specifying individual fw_cfg entries without explicitly
>> giving an index, but is not something that is visible in either the host or
>> guest file system. Is this about right? In my code I’m using “/etc/vmgenid”
>
> yes
>
>> As for the blob, I’m thinking this is where my main problem is. The
>> ‘fw_cfg_add_*()’ functions take a data pointer but doesn’t seem to copy the
>> data anywhere. We pass essentially a pointer via ACPI to the guest, so what
>> it points to needs to be in an accessible region. I don’t get how to define
>> the blob contents. There are command-line ‘fw-cfg’ options where you can
>> specify a file, but it’s not clear to me how to use them. Maybe I reserve
>> some IO memory or something?
>
> Not sure I understand the question. fw cfg device will make
> memory accessible to guest. Put the guest physical address there.
> the address needs to be calculated by linker.
>
I’m almost ready to submit a V2 of the patch set, but there’s still one issue
that I can’t figure out. From the guest, I can read the contents of the blob.
If I make a change to the contents of the blob (via QMP) the guest does not see
the changes. Is there something I need to do on the QEMU side to “push” the
updated fw_cfg contents to the guest? I’ve noticed this both when writing a
qtest for the feature, and also in a Linux kernel module I wrote that reads the
ACPI contents in a guest.
thanks,
Ben
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- Re: [Qemu-devel] Virtual Machine Generation ID,
Ben Warren <=
- Re: [Qemu-devel] Virtual Machine Generation ID, Igor Mammedov, 2017/01/16
- Re: [Qemu-devel] Virtual Machine Generation ID, Michael S. Tsirkin, 2017/01/16
- Re: [Qemu-devel] Virtual Machine Generation ID, Ben Warren, 2017/01/16
- Re: [Qemu-devel] Virtual Machine Generation ID, Igor Mammedov, 2017/01/17
- Re: [Qemu-devel] Virtual Machine Generation ID, Ed Swierk, 2017/01/17
- Re: [Qemu-devel] Virtual Machine Generation ID, Michael S. Tsirkin, 2017/01/17
- Re: [Qemu-devel] Virtual Machine Generation ID, Ed Swierk, 2017/01/17
- Re: [Qemu-devel] Virtual Machine Generation ID, Michael S. Tsirkin, 2017/01/17
- Re: [Qemu-devel] Virtual Machine Generation ID, Ben Warren, 2017/01/17
- Re: [Qemu-devel] Virtual Machine Generation ID, Igor Mammedov, 2017/01/17