[Bug 213257] New: KVM-PR: FPU is broken when single-stepping

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=213257

            Bug ID: 213257
           Summary: KVM-PR: FPU is broken when single-stepping
           Product: Virtualization
           Version: unspecified
    Kernel Version: 5.6
          Hardware: PPC-64
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
          Assignee: virtualization_kvm@kernel-bugs.osdl.org
          Reporter: cand@gmx.com
        Regression: No

The FPU is completely broken when single-stepping on KVM-PR. Registers stay
zeroes, computation results are zeroes. If I disable single-stepping,
computation results are correct, but of course then I cannot dump FPRs between
every instruction.

HW is POWER9, 18-core Talos II.

5.6 is slightly old, but there are no commits under arch/powerpc/kvm since that
mention single stepping.

Program:
https://git.libre-soc.org/?p=kvm-minippc.git;a=summary

Test file:
https://ftp.libre-soc.org/mini-float-test-kvm.bin

Repro instructions:
git clone https://git.libre-soc.org/git/kvm-minippc.git
cd kvm-minippc
make

wget https://ftp.libre-soc.org/mini-float-test-kvm.bin
./kvm-minippc -i mini-float-test-kvm.bin -t trace
less trace
# you will see FPRs stay zeroes. In larger test programs that dump the computed
memory, that is wrong too (all zero).

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