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

[Kevin O'Connor <kevin@koconnor.net>]

On Tue, Dec 22, 2015 at 02:14:12AM +0000, Gonglei (Arei) wrote:
> > From: Kevin O'Connor [mailto:kevin@koconnor.net]
> > Sent: Tuesday, December 22, 2015 2:47 AM
> > To: Gonglei (Arei)
> > Cc: Xulei (Stone); Paolo Bonzini; qemu-devel; seabios@seabios.org;
> > Huangweidong (C); kvm@vger.kernel.org; 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?

> > 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.

-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