Re: [Xen-devel] Xen-4.3 - curious crash

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-01-29 at 09:01 +0000, Jan Beulich wrote:
> >>> On 29.01.14 at 09:51, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Wed, 2014-01-29 at 08:43 +0000, Jan Beulich wrote:
> >> An interrupt not properly restoring EFLAGS.IF (or actually one not
> >> properly restoring all of EFLAGS) would be very odd. About as odd
> >> as a cosmic radiation induced bit flip resulting in some other
> >> misbehavior.
> > 
> > Isn't it also the affect of a missing spin_unlock(_irqrestore)? Or does
> > something else catch that first?
> 
> A missing plain spin_unlock() wouldn't have any effect of IF. And
> a missing spin_unlock_irqrestore() would have an effect on IF in
> the interrupt handler, but with the return being through an IRET
> something would need to actively modify the flags on the stack
> that IRET uses in order to affect the interrupted code's EFLAGS.

Ah, I mistakenly thought that this issue was happening on that return
path (i.e. before the IRET).

Ian.


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