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Date: Wed, 29 Sep 2021 11:24:02 +0100
From: "Richard W.M. Jones" <rjones@redhat.com>
To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= <berrange@redhat.com>
Subject: Re: [PATCH 0/1] vmx: Fix <genid/> mapping
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On Wed, Sep 29, 2021 at 11:07:30AM +0100, Daniel P. Berrangé wrote:
> I'm not sure if we actually need the full driver or not for testing
> purposes. The the GenID is just in memory somewhere, and the somewhere
> is reported via ACPI table entry. For QEMU its easy as the data is
> exposed via fw_cfg which can be read from sysfs directly without
> even needing to look at ACPI entries to find it. Not sure how we
> find it with VMWare/HyperV though.

This still has the problem that qemu is mangling the vmgenid.
Nevertheless, on qemu-6.1.0-5.fc36.x86_64 I added this to a Linux
guest:

  <genid>11223344-5566-7788-99aa-bbccddeeff00</genid>

which turned into:

  -device vmgenid,guid=11223344-5566-7788-99aa-bbccddeeff00,id=vmgenid0

Inside the guest:

# ls /sys/firmware/qemu_fw_cfg/by_name/etc/vmgenid_guid/ -l
total 0
-r--------. 1 root root 4096 Sep 29 11:16 key
-r--------. 1 root root 4096 Sep 29 11:16 name
-r--------. 1 root root    0 Sep 29 11:16 raw
-r--------. 1 root root 4096 Sep 29 11:16 size
# hexdump -C /sys/firmware/qemu_fw_cfg/by_name/etc/vmgenid_guid/raw 
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000020  00 00 00 00 00 00 00 00  44 33 22 11 66 55 88 77  |........D3".fU.w|
00000030  99 aa bb cc dd ee ff 00  00 00 00 00 00 00 00 00  |................|
00000040  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00001000


But I think what I really need to do is look at the raw physical
address:

# hexdump -C /sys/firmware/qemu_fw_cfg/by_name/etc/vmgenid_addr/raw 
00000000  28 f0 ff 7f 00 00 00 00                           |(.......|
00000008

# dd if=/dev/mem bs=1 skip=$(( 0x7ffff028 )) count=16 | hexdump -C
16+0 records in
16+0 records out
16 bytes copied, 6.0392e-05 s, 265 kB/s
00000000  44 33 22 11 66 55 88 77  99 aa bb cc dd ee ff 00  |D3".fU.w........|
00000010


I think for VMware I'm really going to need the kernel driver, unless
there's some way that iasl can be used to extract the information?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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