On Fri, Oct 30, 2026 at 10:00:50PM +0530, Ritesh Harjani wrote: > > Hi Shrikanth, > > Shrikanth Hegde <[email protected]> writes: > > > After applying preempt disable patch, i.e PATCH 1/2, Christian reported > > a subsequent warning stopping his board to boot properly. > > > > WARNING: at .kvmppc_fix_ee_before_entry+0x10/0x28, CPU#0: > > qemu-system-ppc/4667 > > CPU: 0 UID: 1000 PID: 4667 Comm: qemu-system-ppc Tainted: G W > > 7.3.0-rc4-2-powerpc64-smp #1 PREEMPT > > Tainted: [W]=WARN > > Hardware name: varisys,CYRUS5040 e5500 0x80240012 CoreNet Generic > > NIP [c00000000005dc3c] .kvmppc_fix_ee_before_entry+0x10/0x28 > > LR [c00000000005f298] .kvmppc_handle_exit+0x5b4/0x5e8 > > Call Trace: > > [c000000086587780] [c00000000005ee10] .kvmppc_handle_exit+0x12c/0x5e8 > > (unreliable) > > [c000000086587830] [c000000000062068] .kvmppc_resume_host+0xb8/0x10c > > > > It triggers below warning... > > > > static inline void kvmppc_fix_ee_before_entry(void) > > { > > trace_hardirqs_on(); > > > > /* > > * To avoid races, the caller must have gone directly from having > > * interrupts fully-enabled to hard-disabled. > > */ > > WARN_ON(local_paca->irq_happened != PACA_IRQ_HARD_DIS); > > > > This happens since kvmppc_prepare_to_enter does first local_irq_disable > > followed by hard_irq_disable. This leaves a small window where interrupt > > may occur and it could set the irq pending bit in PACA. When that > > happens replay that interrupt before entering the guest. > > > > Fixes: 12013e3d4695 ("KVM: powerpc: Use generic xfer to guest work > > function") > > Reported-by: Christian Zigotzky <[email protected]> > > Closes: > > https://lore.kernel.org/all/[email protected]/ > > Signed-off-by: Shrikanth Hegde <[email protected]> > > --- > > arch/powerpc/kvm/powerpc.c | 13 +++++++++++++ > > 1 file changed, 13 insertions(+) > > > > diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c > > index 9194cf492d1c..847ff07c364b 100644 > > --- a/arch/powerpc/kvm/powerpc.c > > +++ b/arch/powerpc/kvm/powerpc.c > > @@ -147,6 +147,19 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu) > > continue; > > } > > > > +#ifdef CONFIG_PPC64 > > + /* > > + * Interrupt arrived between the soft and hard > > + * disable. Replay it and retry guest entry. > > + */ > > + if (unlikely(local_paca->irq_happened != PACA_IRQ_HARD_DIS)) { > > + local_irq_enable(); > > + local_irq_disable(); > > + hard_irq_disable(); > > + continue; > > + } > > +#endif > > + > > I looked at the commit which causes this regression, I see there are few > more call sites which can hit the same WARN in kvmppc_fix_ee_before_entry(). > > So what I was thinking was - while we are at it - do you think we could > use the following helper instead of {local|hard}_irq_{disable|enable}() > pair and ... > > > /* > * Hard disable interrupts before entering the guest. > * > * On 64-bit don't use local_irq_disable() here. It only soft-masks, so > * an interrupt can still come in before we hard disable. That interrupt > * gets marked pending in irq_happened and kvmppc_fix_ee_before_entry() > * then throws it away. hard_irq_disable() clears MSR[EE] first and does > * the irq tracing itself, so there's no such window. > * > * On 32-bit there is no soft mask and hard_irq_disable() doesn't do the > * irq tracing, so use local_irq_disable(). > */ > static inline void kvmppc_irq_disable_for_entry(void) > { > #ifdef CONFIG_PPC64 > hard_irq_disable(); > #else > local_irq_disable(); > #endif > } > > ... and then update the other call sites too which the following commit > added - which can cause the WARN. > Fixes: 12013e3d4695 ("KVM: powerpc: Use generic xfer to guest work > function") > > Thoughts? > Yeah, i also feel this is better to have. Personally i don't want this ifdef all around the code, It's better to have it in one place. There's one more case like this here[1].
[1]https://lore.kernel.org/all/a14571be1897955f43d9994f0e093de3ada6ecde.1793447880.git.ritesh.l...@gmail.com/ Regards, Mukesh > -ritesh > > > guest_enter_irqoff(); > > return 1; > > } > > -- > > 2.52.0
