On 9/25/25 19:17, Zhao Liu wrote:
On Tue, Sep 23, 2025 at 12:41:34PM +0200, Paolo Bonzini wrote:
Date: Tue, 23 Sep 2025 12:41:34 +0200
From: Paolo Bonzini <[email protected]>
Subject: [RFT PATCH v2 0/2] Fix cross migration issue with missing
features: pdcm, arch-capabilities
X-Mailer: git-send-email 2.51.0
Add two compatibility properties to restore legacy behavior of machine types
prior to QEMU 10.1. Each of them addresses the two changes to CPUID:
- ARCH_CAPABILITIES should not be autoenabled when the CPU model specifies AMD
as the vendor
- specifying PDCM without PMU now causes an error, instead of being silently
dropped in cpu_x86_cpuid.
Note, I only tested this lightly.
Sorry for late.
I found the previous 2 fixes were merged into stable 10.0:
24778b1c7ee7aca9721ed4757b0e0df0c16390f7
3d26cb65c27190e57637644ecf6c96b8c3d246a3
Should stable 10.0 revert these 2 fixes, to ensure migration
compatibility?
Now when I think about it.
There were at least 2 point releases of 10.0.x (10.0.4 & 10.0.5)
with these 2 patches already. Reverting them in 10.0 will make
10.0 to be non-migratable with itself (10.0.5 can't be migrated
to 10.0.6 if we'll release 10.0.6 with these 2 patches reverted).
Also, as far as I can see (and I asked about this some 5 times
already, with no one answering - is it that difficult?) - we
should pick this series (pdcm, arch-capabilities) to 10.1.x stable
series too, since we can't migrate from previous versions to 10.1
which has the two changes mentioned above.
It looks to me - since the breakage is already done, and both 10.0
and 10.1 is broken, we should declare the current situation as a
status quo, and do the following:
1. keep the above mentioned 24778b1c7ee7a and 3d26cb65c27190e5 in
10.0.x (instead of reverting them);
2. pick up this 2 patches (fix cross migration issue with missing
pdcm, arch-capabilities) to 10.1.x (it should be done either way,
I think);
3. on top of these 2 "missing features: pdcm, arch-capabilities",
make the crossing line for before-10.0, not for before-10.1 series, -
ie, consider 10.0 *also* has these properties, but 9.2 and before
are not.
This too will make 10.0.5 => 10.0.6 non-migrateable, just like if
I'll revert 24778b1c7ee7a and 3d26cb65c27190e5 in 10.0. But this way
we will also have these bugs fixed in 10.0. And all subsequent
versions of 10.0 and 10.1 will be migratable again.
Please, don't be quiet this time, - I need your comments for this
matter, because I don't understand well enough how migration works.
Cc'ing Peter too, because I'm stuck here and no my questions are
getting answered.. maybe he can help to at least clear some questions.
Thanks,
/mjt
