[Bug 217799] kvm: Windows Server 2003 VM fails to work on 6.1.44 (works fine on 6.1.43)

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=217799

--- Comment #3 from Roman Mamedov (rm+bko@romanrm.net) ---
Hello,

Unfortunately I am not in a position to easily do bisects.
But as noted above, setting "spec_rstack_overflow=off" is enough to solve it.

Further info, trying with an XP x64 install ISO provided by Microsoft:
https://archive.org/details/windows-xp-professional-x64-edition

With "spec_rstack_overflow=off", it works fine. But in the default state of
this new mitigation (which is "safe RET, no microcode" on my machine), the
install ISO hangs at the "Setup is starting Windows" message. So if anyone
wants to reproduce on their local machine, there is now a quick and legal way
to do so.

My QEMU command-line:

kvm -cpu host -m 2048 -machine pc,mem-merge=on,accel=kvm -vnc [::]:24 -device
ide-hd,drive=drive0,bus=ide.0 -drive
if=none,id=drive0,cache=writeback,aio=threads,format=raw,discard=unmap,detect-zeroes=off,file=xp.img
-rtc base=localtime -cdrom xp64ce.iso -boot d

I should add that when a VM is in this stuck state, the CPU load by QEMU
process is 0% (not 100%).

And I am not sure why the default mitigation state says "no microcode", as I
use a 2023-08-08 updated microcode package from Debian.

# dmesg | grep microcode
[    0.401618] Speculative Return Stack Overflow: IBPB-extending microcode not
applied!
[    0.401618] Speculative Return Stack Overflow: Mitigation: safe RET, no
microcode
[    1.051941] microcode: CPU0: patch_level=0x0a201016
[    1.051947] microcode: CPU1: patch_level=0x0a201016
[    1.051953] microcode: CPU2: patch_level=0x0a201016
[    1.051960] microcode: CPU3: patch_level=0x0a201016
[    1.051967] microcode: CPU4: patch_level=0x0a201016
[    1.051973] microcode: CPU5: patch_level=0x0a201016
[    1.051981] microcode: CPU6: patch_level=0x0a201016
[    1.051989] microcode: CPU7: patch_level=0x0a201016
[    1.051996] microcode: CPU8: patch_level=0x0a201016
[    1.052003] microcode: CPU9: patch_level=0x0a201016
[    1.052010] microcode: CPU10: patch_level=0x0a201016
[    1.052018] microcode: CPU11: patch_level=0x0a201016
[    1.052024] microcode: CPU12: patch_level=0x0a201016
[    1.052030] microcode: CPU13: patch_level=0x0a201016
[    1.052036] microcode: CPU14: patch_level=0x0a201016
[    1.052041] microcode: CPU15: patch_level=0x0a201016
[    1.052046] microcode: CPU16: patch_level=0x0a201016
[    1.052052] microcode: CPU17: patch_level=0x0a201016
[    1.052058] microcode: CPU18: patch_level=0x0a201016
[    1.052064] microcode: CPU19: patch_level=0x0a201016
[    1.052070] microcode: CPU20: patch_level=0x0a201016
[    1.052076] microcode: CPU21: patch_level=0x0a201016
[    1.052082] microcode: CPU22: patch_level=0x0a201016
[    1.052088] microcode: CPU23: patch_level=0x0a201016
[    1.052092] microcode: Microcode Update Driver: v2.2.

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