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

[Kevin O'Connor]

On Sat, Dec 19, 2015 at 12:03:15PM +0000, Gonglei (Arei) wrote:
> Maybe the root cause is not NMI but INTR, so yield() can open hardware interrupt,
> And then execute interrupt handler, but the interrupt handler make the SeaBIOS
> stack broken, so that the BSP can't execute the instruction and occur exception,
> VM_EXIT to Kmod, which is an infinite loop. But I don't have any proofs except
> the surface phenomenon.

I can't see any reason why allowing interrupts at this location would
be a problem.
> Kevin, can we drop yield() in smp_setup() ?

It's possible to eliminate this instance of yield, but I think it
would just push the crash to the next time interrupts are enabled.
> Is it really useful and allowable for SeaBIOS? Maybe for other components?
> I'm not sure. Because we found that when SeaBIOS is booting, if we inject a
> NMI by QMP, the guest will *stuck*. And the kvm tracing log is the same with
> the current problem.

If you apply the patches you had to prevent that NMI crash problem,
does it also prevent the above crash?

-Kevin

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

[Gonglei (Arei)]

> -----Original Message-----
> From: Kevin O'Connor [mailto:[e-mail]]
> Sent: Saturday, December 19, 2015 11:12 PM
> On Sat, Dec 19, 2015 at 12:03:15PM +0000, Gonglei (Arei) wrote:
> > Maybe the root cause is not NMI but INTR, so yield() can open hardware
> > interrupt,
> > And then execute interrupt handler, but the interrupt handler make the
> > SeaBIOS
> > stack broken, so that the BSP can't execute the instruction and occur
> > exception,
> > VM_EXIT to Kmod, which is an infinite loop. But I don't have any proofs except
> > the surface phenomenon.
>
> I can't see any reason why allowing interrupts at this location would
> be a problem.

Does it have any relationship with *extra stack* of SeaBIOS?
> > Kevin, can we drop yield() in smp_setup() ?
>
> It's possible to eliminate this instance of yield, but I think it
> would just push the crash to the next time interrupts are enabled.

Perhaps. I'm not sure.
> > Is it really useful and allowable for SeaBIOS? Maybe for other components?
> > I'm not sure. Because we found that when SeaBIOS is booting, if we inject a
> > NMI by QMP, the guest will *stuck*. And the kvm tracing log is the same with
> > the current problem.
>
> If you apply the patches you had to prevent that NMI crash problem,
> does it also prevent the above crash?

Yes, but we cannot prevent the NMI injection (though I'll submit some patches to
forbid users' NMI injection after NMI_EN disabled by RTC bit7 of port 0x70).


Regards,
-Gonglei