Re: [PATCH v3 2/3] KVM: PPC: BookE: Load FP and Altivec before enabling the interrupts

[IBM]

Shrikanth Hegde <sshegde@xxxxxxxxxxxxx> writes:

> Christian reported that booting preemptible kernel on FSL Cyrus+ board
> causes boot hang.
>
> The logs pointed that system was busy in printing below warning.
>
> WARNING: at .enable_kernel_fp+0x30/0x78, CPU#3: qemu-system-ppc/4884
> Modules linked in:
> CPU: 3 UID: 1000 PID: 4884 Comm: qemu-system-ppc Not tainted 7.3.0-rc1-powerpc64-smp-preempt #1 PREEMPT
> NIP [c000000000003338] .enable_kernel_fp+0x30/0x78
> LR [c00000000005de84] .kvmppc_load_guest_fp+0x30/0x80
> Call Trace:
> [c000000085ca7700] [c00000000005de84] .kvmppc_load_guest_fp+0x30/0x80
> [c000000085ca7780] [c00000000005f2a0] .kvmppc_handle_exit+0x5bc/0x5cc
> [c000000085ca7830] [c00000000006204c] .kvmppc_resume_host+0xb8/0x10c
>
> Which is...
>
> void enable_kernel_fp(void)
> {
>         unsigned long cpumsr;
>         WARN_ON(preemptible());
>
> And...
>
> Though irq's are hard disabled after kvmppc_prepare_to_enter, but
> kvmppc_fix_ee_before_entry enables the softmask's IRQ state.
> That causes the irqs_disabled to return false.
> Hence leading to the warnings.
>
> Fix it by re-ordering the code to load the FP and Altivec
> before enabling the softmask IRQ state.
>
> Suggested-by: Narayana Murty N <nnmlinux@xxxxxxxxxxxxx>
> Fixes: 3efc7da61f6c ("KVM: PPC: Book3E: Increase FPU laziness")
> Reported-by: Christian Zigotzky <chzigotzky@xxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/33342fbf-eb7b-bde6-2c8c-254fe8bfb993@xxxxxxxxxxx/
> Tested-by: Christian Zigotzky <chzigotzky@xxxxxxxxxxx>
> Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@xxxxxxxxx>
> Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
> ---
>  arch/powerpc/kvm/booke.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

LGTM. So, please feel free to add:
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>