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([2001:b07:6468:f312:bc4e:7fe8:2916:6a59]) by smtp.gmail.com with ESMTPSA id q68sm3371147wme.14.2020.01.08.01.36.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Jan 2020 01:36:57 -0800 (PST) Subject: Re: discuss about pvpanic To: zhenwei pi Cc: "yelu@bytedance.com" , Greg KH , qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, Michal Privoznik , "libvir-list@redhat.com" References: <2feff896-21fe-2bbe-6f68-9edfb476a110@bytedance.com> From: Paolo Bonzini Message-ID: Date: Wed, 8 Jan 2020 10:36:56 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <2feff896-21fe-2bbe-6f68-9edfb476a110@bytedance.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/01/20 09:25, zhenwei pi wrote: > Hey, Paolo > > Currently, pvpapic only supports bit 0(PVPANIC_PANICKED). > We usually expect that guest writes ioport (typical 0x505) in panic_notifier_list callback > during handling panic, then we can handle pvpapic event PVPANIC_PANICKED in QEMU. > > On the other hand, guest wants to handle the crash by kdump-tools, and reboots without any > panic_notifier_list callback. So QEMU only knows that guest has rebooted (because guest > write 0xcf9 ioport for RCR request), but QEMU can't identify why guest resets. > > In production environment, we hit about 100+ guest reboot event everyday, sadly we > can't separate the abnormal reboot from normal operation. > > We want to add a new bit for pvpanic event(maybe PVPANIC_CRASHLOADED) to represent the guest has crashed, > and the panic is handled by the guest kernel. (here is the previous patch https://lkml.org/lkml/2019/12/14/265) > > What do you think about this solution? Or do you have any other suggestions? Hi Zhenwei, the kernel-side patch certainly makes sense. I assume that you want the event to propagate up from QEMU to Libvirt and so on? The QEMU patch would need to declare a new event (qapi/misc.json) and send it in handle_event (hw/misc/pvpanic.c). For Libvirt I'm not familiar, so I'm adding the respective list. Another possibility is to simply not write to pvpanic if kexec_crash_loaded() returns true; this would match what xen_panic_event does for example. The kexec kernel would then log the panic normally, without the need for MMIO at all. However, I have no problem with adding a new bit to the pvpanic I/O port so once you post the QEMU patch I will certainly ack the kernel side. Thanks, Paolo