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Wed, 23 Sep 2026 07:09:15 +0200 (CEST) Subject: Re: [Linux PPC] Disable PREEMPT To: Shrikanth Hegde , =?UTF-8?Q?Michal_Such=c3=a1nek?= Cc: "Christophe Leroy (CS GROUP)" , Michael Ellerman , harshpb@linux.ibm.com, Gautam Menghani , amachhiw@linux.ibm.com, linuxppc-dev , "kvm-ppc@vger.kernel.org" , Madhavan Srinivasan , Peter Zijlstra , "R.T.Dickinson" , hypexed@yahoo.com.au, mad skateman , Christian Zigotzky , Samir M , Venkat Rao Bagalkote , Narayana Murty N , Hari Bathini References: <25cf64ab-2a32-4d4c-a0c7-2e9007c276d4@linux.ibm.com> <9b58bd58-d0e4-463e-bff9-e33b153b2987@linux.ibm.com> <7ad57b61-4567-42c8-a9f6-faaabe7766a7@linux.ibm.com> <7e06fb84-ca2e-dbb4-47bd-e95ee11113c9@xenosoft.de> <79f9d4e3-ce55-d238-e4a9-b11e9ce27c5f@xenosoft.de> <33342fbf-eb7b-bde6-2c8c-254fe8bfb993@xenosoft.de> From: Christian Zigotzky Organization: A-EON Open Source Message-ID: <7fb5baa6-9d06-2c61-2b43-6835e8fb0d1a@xenosoft.de> Date: Wed, 23 Sep 2026 07:09:14 +0200 X-Mailer: BrassMonkey/34.3.2.1 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 21/09/26 07:12, Shrikanth Hegde wrote: > Hi Christian. > > On 9/20/26 6:34 PM, Christian Zigotzky wrote: >> On 09/20/2026 01:49 PM, Christian Zigotzky wrote: >>> On 09/18/2026 09:10 AM, Michal Suchánek wrote: >>>> On Fri, Sep 18, 2026 at 04:39:57AM +0200, Christian Zigotzky wrote: >>>>> On 17/09/26 16:15, Shrikanth Hegde wrote: >>>>>> Hi Michal, >>>>>> >>>>>>>> Give it a try. >>>>>>>> >>>>>>>> I am suspecting both lockup, stack corruptions are secondary >>>>>>>> symptoms here. >>>>>>>> While recreate, I have different type of traces. >>>>>>> Yes, it does work for the crash I see. >>>>>> Thanks. Give me sometime to see further on that. Didn't get any time >>>>>> today. >>>>>> >>>>>>> However, we hijacked the report >>>>>>> of KVM locking up on FSL Cyrus+, and that is likely a different >>>>>>> problem >>>>>>> still not addressed. >>>>>>> >>>>>> Ah, that's what you meant. Yes, i still don't know where FSL >>>>>> Cyrus+ is >>>>>> stuck. >>>>>> >>>>>> I would need help from FSL Cyrus+ to get some logs or is there a >>>>>> way we >>>>>> can spin of >>>>>> a QEMU guest of it? We should have the log to start somewhere. >>>>>> >>>>>> >>>>> It's difficult to get a log because it freezes and can't write any >>>>> error >>>>> messages to the log files. This bug is very old. We had this issue >>>>> some >>>>> years ago but we was able to disable PREEMPT because we don't need >>>>> it. >>>> I would expect serial console and sysrq could give something, >>>> depending >>>> on how much of the kernel is frozen. >>>> >>>> Thanks >>>> >>>> Michal >>> Here is a serial log: >>> https://github.com/user-attachments/files/32433586/e5500_preempt_putty.log >>> > > Thanks Michal for helping to get the traces. > >> Another serial log with pcie_ports=compat: >> https://github.com/user-attachments/files/32434487/e5500_preempt_pcie_ports_compat_putty.log >> >> > > I see it is mostly busy with printing > WARNING: at .enable_kernel_fp+0x30/0x78, CPU#3: qemu-system-ppc/4884 > > The path seems to be same also. > > [c000000085ca7700] [c00000000005de84] .kvmppc_load_guest_fp+0x30/0x80 > [c000000085ca7780] [c00000000005f2a0] .kvmppc_handle_exit+0x5bc/0x5cc > [c000000085ca7830] [c00000000006204c] .kvmppc_resume_host+0xb8/0x10c > > > Does below help to boot or make it stable? > --- >  arch/powerpc/kvm/booke.c | 9 ++++++++- >  1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c > index 13ad4cf5fa71..d4be7a306bfc 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 */ > +            /* > +             * interrupts now hard-disabled. i.e EE=0 > +             * But irqs_disabled relies on PACA entries > +             * and fixup below enables it. > +             * So irqs_disabled == false > +             */ >              kvmppc_fix_ee_before_entry(); > +            preempt_disable(); >              kvmppc_load_guest_fp(vcpu); >              kvmppc_load_guest_altivec(vcpu); > +            preempt_enable_no_resched(); >          } >      } > > Hi, Thanks a lot for your patch! I patched the 7.3-rc4 kernel sources with your new patch and compiled the kernel again yesterday. [1] Unfortunately, the issue still exists. I tested it with a guest kernel with and without preempt support. Cheers, Christian [1] https://github.com/chzigotzky/kernels/releases/tag/v7.3.0-rc4-2-preempt -- Sent with BrassMonkey 34.3.2.1 (https://github.com/chzigotzky/Web-Browsers-and-Suites-for-Linux-PPC/releases/tag/BrassMonkey_34.3.2.1)