[PATCH v2 2/3] KVM: PPC: BookE: Load FP and Altivec before enabling the interrupts

[Shrikanth Hegde <sshegde@linux.ibm.com>]

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 <chzigotzky@xenosoft.de>
Closes: https://lore.kernel.org/all/33342fbf-eb7b-bde6-2c8c-254fe8bfb993@xenosoft.de/
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 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.
+			 */
 			kvmppc_load_guest_fp(vcpu);
 			kvmppc_load_guest_altivec(vcpu);
+			kvmppc_fix_ee_before_entry();
 		}
 	}
 
-- 
2.52.0