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

[Narayana Murty N <nnmlinux@linux.ibm.com>]

Hi Shrikanth,

On 12/11/26 6:39 PM, 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.
> 
> Suggested-by: Narayana Murty N <nnmlinux@linux.ibm.com>
> Fixes: 3efc7da61f6c ("KVM: PPC: Book3E: Increase FPU laziness")
> Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
> Closes: https://lore.kernel.org/all/33342fbf-eb7b-bde6-2c8c-254fe8bfb993@xenosoft.de/
> Tested-by: Christian Zigotzky <chzigotzky@xenosoft.de>
> Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>   arch/powerpc/kvm/booke.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index 13ad4cf5fa71..aed7b476b7eb 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -1404,10 +1404,9 @@ 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();
>   			kvmppc_load_guest_fp(vcpu);
>   			kvmppc_load_guest_altivec(vcpu);
> +			kvmppc_fix_ee_before_entry();
>   		}
>   	}
>   

This address my previous comment, feel free to add Reviewed-by Narayana 
Murty N <nnmlinux@linux.ibm.com>

thanks,
Narayana.