Re: [Qemu-devel] [PATCH] SeaBios: Fix reset procedure reentrancy problem on qemu-kvm platform

[Gonglei (Arei)]

> -----Original Message-----
> From: Kevin O'Connor [mailto:address@hidden
> Sent: Tuesday, December 22, 2015 11:51 PM
> To: Gonglei (Arei)
> Cc: Xulei (Stone); Paolo Bonzini; qemu-devel; address@hidden;
> Huangweidong (C); address@hidden; Radim Krcmar
> Subject: Re: [Qemu-devel] [PATCH] SeaBios: Fix reset procedure reentrancy
> problem on qemu-kvm platform
> 
> On Tue, Dec 22, 2015 at 02:14:12AM +0000, Gonglei (Arei) wrote:
> > > From: Kevin O'Connor [mailto:address@hidden
> > > Sent: Tuesday, December 22, 2015 2:47 AM
> > > To: Gonglei (Arei)
> > > Cc: Xulei (Stone); Paolo Bonzini; qemu-devel; address@hidden;
> > > Huangweidong (C); address@hidden; Radim Krcmar
> > > Subject: Re: [Qemu-devel] [PATCH] SeaBios: Fix reset procedure reentrancy
> > > problem on qemu-kvm platform
> > >
> > > On Mon, Dec 21, 2015 at 09:41:32AM +0000, Gonglei (Arei) wrote:
> > > > When the gurb of OS is booting, then the softirq and C function
> > > > send_disk_op() may use extra stack of SeaBIOS. If we inject a NMI,
> > > > romlayout.S: irqentry_extrastack is invoked, and the extra stack will
> > > > be used again. And the stack of first calling will be broken, so that 
> > > > the
> > > SeaBIOS stuck.
> > > >
> > > > You can easily reproduce the problem.
> > > >
> > > > 1. start on guest
> > > > 2. reset the guest
> > > > 3. inject a NMI when the guest show the grub surface 4. then the guest
> > > > stuck
> > >
> > > Does the SeaBIOS patch below help?
> >
> > Sorry, it doesn't work. What's worse is we cannot stop SeaBIOS stuck by
> > Setting "CONFIG_ENTRY_EXTRASTACK=n" after applying this patch.
> 
> Oops, can you try with the patch below instead?
> 

It works now. Thanks!

But do we need to check other possible situations
that maybe cause *extra stack* broken or overridden?


> > > I'm not familiar with how to "inject a
> > > NMI" - can you describe the process in more detail?
> > >
> >
> > 1. Qemu Command line:
> >
> > #: /home/qemu/x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 4096
> -smp 8 -name suse -vnc 0.0.0.0:10 \
> > -device virtio-scsi-pci,id=scsi0 -drive
> file=/home/suse11_sp3_32_2,if=none,id=drive-scsi0-0-0-0,format=raw,cache=
> none,aio=native \
> > -device scsi-hd,bus=scsi0.0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0 \
> > -chardev file,id=seabios,path=/home/seabios.log -device
> isa-debugcon,iobase=0x402,chardev=seabios \
> > -monitor stdio -qmp unix:/tmp/qmp,server,nowait
> >
> > 2. Inject a NMI by QMP:
> >
> > #: /home/qemu/scripts/qmp # ./qmp-shell /tmp/qmp
> > Welcome to the QMP low-level shell!
> > Connected to QEMU 2.5.0
> >
> > (QEMU) system_reset
> > {"return": {}}
> > (QEMU) inject-nmi
> > {"return": {}}
> > (QEMU) inject-nmi
> > {"return": {}}
> >
> 
> I tried a few simple tests but was not able to reproduce.
> 
After reset the guest, then you inject an NMI when you see the grub surface
ASAP. 

Kevin, I sent you a picture in private. :)


Regards,
-Gonglei

> -Kevin
> 
> 
> --- a/src/romlayout.S
> +++ b/src/romlayout.S
> @@ -548,7 +548,10 @@ entry_post:
>          ENTRY_INTO32 _cfunc32flat_handle_post   // Normal entry point
> 
>          ORG 0xe2c3
> -        IRQ_ENTRY 02
> +        .global entry_02
> +entry_02:
> +        ENTRY handle_02  // NMI handler does not switch onto extra stack
> +        iretw
> 
>          ORG 0xe3fe
>          .global entry_13_official