[PATCH 3/7] KVM: PPC: Explicitly force IPIs when directly kicking vCPUs

[Gautam Menghani]

On Fri, Oct 30, 2026 at 11:57:10AM -0700, Sean Christopherson wrote:
> On Fri, Oct 30, 2026, Gautam Menghani wrote:
> > On Wed, Oct 28, 2026 at 12:02:55PM -0700, Sean Christopherson wrote:
> > > Explicitly force an IPI when invoking kvm_vcpu_kick() directly instead of
> > > relying on kvm_arch_vcpu_should_kick() to unconditionally return 1/true.
> > > This will allow dropping kvm_arch_vcpu_should_kick() in favor of
> > > kvm_request_needs_ipi().
> > > 
> > > No functional change intended (1 || 1 == true).
> > > 
> > > Signed-off-by: Sean Christopherson <seanjc at google.com>
> > > ---
> > >  arch/powerpc/include/asm/kvm_ppc.h | 13 ++++++++++++-
> > >  arch/powerpc/kvm/book3s.c          |  4 ++--
> > >  arch/powerpc/kvm/book3s_pr.c       |  2 +-
> > >  arch/powerpc/kvm/booke.c           |  6 +++---
> > >  arch/powerpc/kvm/e500_emulate.c    |  2 +-
> > >  arch/powerpc/kvm/powerpc.c         |  2 +-
> > >  6 files changed, 20 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> > > index 169ea6a7fbad..bbe7378ad0ef 100644
> > > --- a/arch/powerpc/include/asm/kvm_ppc.h
> > > +++ b/arch/powerpc/include/asm/kvm_ppc.h
> > > @@ -30,6 +30,17 @@
> > >  #endif
> > >  #include <asm/inst.h>
> > >  
> > > +/*
> > > + * TODO: For unknown reasons, KVM PPC has historically ignored vcpu->mode when
> > > + *       determining if kicking a vCPU needs an IPI.  Either document why that
> > > + *       behavior is necessary, or drop this helper and the @force param from
> > > + *       __kvm_vcpu_kick().
> > > + */
> > > +static inline void kvmppc_vcpu_kick(struct kvm_vcpu *vcpu)
> > > +{
> > > +	__kvm_vcpu_kick(vcpu, false, true);
> > > +}
> > > +
> > 
> > AFAICS, there is no reason for PPC to always return 1. I was looking at
> > the old patches on mailing list and found this - https://lore.kernel.org/kvm/0FEE585F-5E21-47F2-A3F0-AD0DE05EBB43@suse.de
> > 
> > ```
> > How about we return 1 for kvm_arch_vcpu_in_guest_mode() on !x86 always, just
> > like it's done today basically? Then we can worry about needless IPIs later
> > and don't regress from the respective current kick implementations.
> > ```
> 
> FWIW, I found that as well, but there are a metric ton of kvm_vcpu_kick() calls
> that have been added since then, and they scared me.
> 
> > However, I'll do some testing and get back by mid next week to make sure
> > there are no suprises.
> 
> Thanks!  If we can drop the PPC behavior, that would be wonderful!  Though if
> we do that, it should be for 7.5 in a follow-up (this series really should go
> into 7.4 due to the SNP issue).


Yeah I looked into it and realized that the newer variants of KVM on PPC
are not even using vcpu->mode at all. So that has to be fixed from our
end.

For this series,
Reviewed-by: Gautam Menghani <gautam at linux.ibm.com> # PPC