linux-kernel - Re: discuss about pvpanic

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Message-ID: <dd8e46c4-eac4-046a-82ec-7ae17df75035@redhat.com>
Date:   Wed, 8 Jan 2020 10:36:56 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     zhenwei pi <pizhenwei@...edance.com>
Cc:     "yelu@...edance.com" <yelu@...edance.com>,
        Greg KH <gregkh@...uxfoundation.org>, qemu-devel@...gnu.org,
        linux-kernel@...r.kernel.org,
        Michal Privoznik <mprivozn@...hat.com>,
        "libvir-list@...hat.com" <libvir-list@...hat.com>
Subject: Re: discuss about pvpanic

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