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a=ed25519-sha256; c=relaxed/relaxed; t=1793521732; s=strato-dkim-0003; d=xenosoft.de; h=In-Reply-To:Date:Message-ID:From:References:Cc:To:Subject:Cc:Date: From:Subject:Sender; bh=vlZRwvKFZngxd4ogQEIfdVGvHi+Ew7cR4JQOBhK+k7I=; b=2SNI8NAnWSJRFlbYf5jySV+sISntx9QURQ4Sge9Og+CQq9Djam9T0GfezkGlL6FT59 qtjUz2mtLaFTK9teCcCw== X-RZG-AUTH: ":L2QefEenb+UdBJSdRCXu93KJ1bmSGnhMdmOod1DhGN0rBVhd9dFr4thIFiqT9BURIi+m7xzg" Received: from void-ppc.a-eon.tld by smtp.strato.de (RZmta 55.6.3 DYNA|AUTH) with ESMTPSA id e825d92A18So4xa (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits)) (Client did not present a certificate); Sun, 1 Nov 2026 09:28:50 +0100 (CET) Subject: Re: [PATCH 1/2] KVM: PPC: BookE: Disable preemption before loading guest FP and Altivec To: "Ritesh Harjani (IBM)" , Shrikanth Hegde , Narayana Murty N , maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org 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, "R.T.Dickinson" , mad skateman , Damien Stewart 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> <33tnw44q.ritesh.list@gmail.com> From: Christian Zigotzky Organization: A-EON Open Source Message-ID: <15075ad5-73f8-4714-0503-2565ca3dfb4b@xenosoft.de> Date: Sun, 1 Nov 2026 09:28:50 +0100 X-Mailer: BrassMonkey/35.0.2 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 In-Reply-To: <33tnw44q.ritesh.list@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_PASS,SPF_PASS autolearn=ham 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 30/10/26 17:21, Ritesh Harjani (IBM) wrote: > 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 > Yes, I can help with testing. - Christian -- Sent with BrassMonkey 35.0.2 (https://github.com/chzigotzky/Web-Browsers-and-Suites-for-Linux-PPC/releases/tag/BrassMonkey_35.0.2)