On Tue, Nov 10, 2026 at 11:02:37AM +0530, Shrikanth Hegde wrote:
> 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.
>
> Fixes: 3efc7da61f6c ("KVM: PPC: Book3E: Increase FPU laziness")
> Reported-by: Christian Zigotzky <[email protected]>
> Closes:
> https://lore.kernel.org/all/[email protected]/
> Signed-off-by: Shrikanth Hegde <[email protected]>
> ---
> arch/powerpc/kvm/booke.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index 13ad4cf5fa71..c35e98d544ec 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -1404,10 +1404,13 @@ int kvmppc_handle_exit(struct kvm_vcpu *vcpu,
> unsigned int exit_nr)
> if (s <= 0)
> r = (s << 2) | RESUME_HOST | (r & RESUME_FLAG_NV);
> else {
> - /* interrupts now hard-disabled */
> - kvmppc_fix_ee_before_entry();
> + /*
> + * Interrupts are still hard disabled and soft enabled
> + * after loading the FP and Altivec.
> + */
nit:
Do we really need this comment here. Moving kvmppc_fix_ee_before_entry
at the end is self explanatory.
> kvmppc_load_guest_fp(vcpu);
> kvmppc_load_guest_altivec(vcpu);
> + kvmppc_fix_ee_before_entry();
> }
> }
>
> --
> 2.52.0
>
Apart from the above nit:
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
