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AKwUvBw9wBM4KJ2c35UGVsT254iePVvIZe1GIlqloHbT+HfFzVtbgYWrqlBkYX8rdr9mrxahBh/tysXF/1h22PkIIL3g@lists.infradead.org X-Gm-Message-State: AFq9FYJzzaqQXNBVrJFCTIo0PZSGJp/Y024Je38yLY6Knrw/13kDT3Ig z0dbTJ/fCjWMKzIhEGFKrXOfZJ40U6kdf78E2eaWZrg66zkCHPGtO17RxhyQN31jf/r7xc9GQah oU2q/YQ== X-Received: from pjbbo5.prod.google.com ([2002:a17:90b:905:b0:3ac:24b3:3484]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:c2c6:b0:3ac:b3c7:de04 with SMTP id 98e67ed59e1d1-3ae897aa752mr1800362a91.34.1793386630946; Fri, 30 Oct 2026 11:57:10 -0700 (PDT) Date: Fri, 30 Oct 2026 11:57:10 -0700 In-Reply-To: X-Archived-By: Mime-Version: 1.0 References: <20261028190259.1819571-1-seanjc@google.com> <20261028190259.1819571-4-seanjc@google.com> Message-ID: Subject: Re: [PATCH 3/7] KVM: PPC: Explicitly force IPIs when directly kicking vCPUs From: Sean Christopherson To: Gautam Menghani Cc: Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Madhavan Srinivasan , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Paolo Bonzini , Fuad Tabba , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Nicholas Piggin , Atish Patra , Alexandre Ghiti , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Stefan Teodorescu Content-Type: text/plain; charset="us-ascii" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261030_115713_549152_50BF374E X-CRM114-Status: GOOD ( 24.30 ) X-Spam-Score: -9.5 (---------) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" X-Spam-Status: No, score=-23.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIMWL_WL_MED,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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 > > --- > > 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 > > > > +/* > > + * 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).