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Fri, 30 Oct 2026 09:28:24 -0700 (PDT) Received: from pve-server ([49.205.216.49]) by smtp.gmail.com with ESMTPSA id 5614622812f47-5640fe0d46dsm1916622b6e.11.2026.10.30.09.28.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Oct 2026 09:28:23 -0700 (PDT) From: Ritesh Harjani (IBM) To: Shrikanth Hegde , Narayana Murty N , maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, chzigotzky@xenosoft.de Cc: mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, linux-kernel@vger.kernel.org, msuchanek@suse.de, harshpb@linux.ibm.com, gautam@linux.ibm.com, amachhiw@linux.ibm.com, venkat88@linux.ibm.com Subject: Re: [PATCH 1/2] KVM: PPC: BookE: Disable preemption before loading guest FP and Altivec In-Reply-To: <2a75097f-6b49-456a-bfef-d5e559ce719a@linux.ibm.com> Date: Fri, 30 Oct 2026 21:51:41 +0530 Message-ID: <33tnw44q.ritesh.list@gmail.com> References: <20260928110411.844582-1-sshegde@linux.ibm.com> <20260928110411.844582-2-sshegde@linux.ibm.com> <9d83e196-4d6b-4be1-811c-eb72527d3cdd@linux.ibm.com> <2a75097f-6b49-456a-bfef-d5e559ce719a@linux.ibm.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , Precedence: list X-Archived-By: MIME-version: 1.0 Content-type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-7.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_PASS,SPF_PASS autolearn=no 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 Shrikanth Hegde writes: > Hi Narayana. > > On 10/1/26 4:56 PM, Narayana Murty N wrote: >> Hi Shrikanth, >> Thanks for the fixes. I had one question on patch 1. > > See response below. > >> >>> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c >>> index 13ad4cf5fa71..5b9118eefe1d 100644 >>> --- a/arch/powerpc/kvm/booke.c >>> +++ b/arch/powerpc/kvm/booke.c >>> @@ -1404,10 +1404,17 @@ 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() marks the software >>> +             * IRQ state enabled while interrupts are still >>> +             * hard-disabled. So disable preemption while loading >>> +             * guest FP and Altivec. >>> +             */ >>>               kvmppc_fix_ee_before_entry(); >>> +            preempt_disable(); >>>               kvmppc_load_guest_fp(vcpu); >>>               kvmppc_load_guest_altivec(vcpu); >>> +            preempt_enable_no_resched(); >> Would it be simpler to move kvmppc_fix_ee_before_entry() after the >> FP/Altivec loads instead? >> >> The normal kvmppc_vcpu_run() entry path already loads the guest >> FP/Altivec state while interrupts are still disabled and calls >> kvmppc_fix_ee_before_entry() immediately before entering the guest. >> >> So could this path follow the same ordering: >> >> kvmppc_load_guest_fp(vcpu); >> kvmppc_load_guest_altivec(vcpu); >> kvmppc_fix_ee_before_entry(); >> Thanks Narayana, that actually make more sense to me. >> That would avoid making the software IRQ state enabled before loading >> the guest FP/Altivec state, and also avoid the additional >> preempt_disable()/preempt_enable_no_resched() pair. >> >> Thanks, >> Narayana Murty. >>>           } >>>       } >> > > I thought I had put that for discussion after ---, but looks like I forgot. > > I don't mind the above too. but I didn't have a way to test it. Actually I agree with Narayan's reasoning here. Sorry for being so late to the game. As you know we have been occupied with other things internally. > So kept it as is based on what Christian said works for him. > If you have a way to test the patches, please let me know. > We can try that too. Let's ask Christian directly :) @Christian - Once we have v2, would you kindly help us test that please? We think the other approach which Narayana suggested might be a better fix for this and it can avoid preempt_enable/disable() dance. However, looks like we may not have the board where we can reproduce this. -ritesh